On the premise that the CEO/CIO/CTO of the company get's his bugs fixed first here's my opinion of what you can tell about who uses what software.

Outlook: Bill is a definite user of Outlook. This is one Microsoft application that gets a lot of attention and enhancement, and in day-to-day use it's fairly stable. The quality climbs above mediocrity. However, Wizards and Rules don't work well, and archiving mail is a feature that often fails. So, you can see that an assistant comes in and prep's Bill's in box, by deleting spam and archiving old mail, before Bill gets in and starts working.

Word: Bill may write a memo or two, and use the reference features, which generally work well. But, Bill never writes a 20 plus page document, or he'd be inundated with system crashes. Since Word does crash we can be sure the CIO of Microsoft doesn't use it.

Access: Bill may have designed small databases in Access, for that it's fine. But, he's never attempted to load a real world sample size into the product or he'd run out of disk space.

PowerPoint: Bill may have tried it once, but that's been it. He's never attempted to build a poster in PowerPoint with 20 to 40 elements on one page. If he did he'd have gone crazy watching PowerPoint reposition his elements auto-magically. I believe he'd have fired the whole PPT team if he were a real user.

Excel: This product I can't speak from personal experience. Word on the web is Excel is inaccurate or off-the-beaten path for statistical use. So, Bill doesn't use it for that. Buy a Real Statistics package. For Example: Excel uses a method to calculate Quartiles( 0%, 25% 50%, 75%, 100% ) not used by any other package, making checking your work with a calculator or other software package a frustrating experience.

VB6 or VB .Net: Bill's not a VB coder. If he had been he'd have been severely burned by Variant behavior, and this feature would have been fixed or dropped. Computers Don't Understand Context. Especially in method signatures.

Java: Bill may have perused the java libraries but, he's doesn't have in depth understanding of the simplicity and beauty of Java or he'd have never attempted to kill it. Bill especially loved the Java.Net library. The functionality of this library brought home to him the need for his own Java clone( .Net ). He never did catch on to Exception handling. But, of course, Microsoft has made a PROFIT CENTER out of support for poorly written software.

C#: If Bill codes, he codes in C#. The nicest language Microsoft has ever written, err, copied. Some speed improvements over Java, the decimal class compared to Java BigInteger and BigDecimal for example.
However, C# still contains one fatal flaw, it takes you nowhere. It locks you into the Windows platform so that other, better, OS's aren't an option. If C# were able to run on Trusted Solaris for example, it would be a viable platform. But, this is what you get with the Microsoft monopoly, no possibility of second sourcing your software on another platform.
- Secondly, Bill doesn't write any threaded code in C#either. Someone forgot what a Class is, Threading is just an API. No inheriting here.
- It looks like Bill is a Com/DCom programmer. Because C# is skitzo. Lot's of IInterfaces hiding under the covers.
- The only way to write clean C# is to write it as if it were Java, and ignore the Interface stuff. Clearly C# is far more complex then it needs to be. This may be necessary to appease the old Com/DCom programmers. This is going to be a battle area. The C/Com programmers are going to write some really ugly and unnecessarily complex stuff. The Java guys are going to write some clean easy to understand stuff. It's a battle of styles. Looks like if Microsoft is your only option then J# is the safest bet for business users. Cutting off the IInterface stuff at the knees and forcing everyone to code to a clean easy to understand style. And that was the reason Java killed C in the first place. With C# having the same weaknesses it's only a matter of time.

Windows Explorer: Bill doesn't search his machine for specific content, because Windows Explorer doesn't find it, even when you know the specific folder to search.

Internet Explorer: Bill doesn't surf the internet or he'd have realized IE is out of date, in poor compliance with standards and is the front door to Windows infection. Poorly designed, no sandbox for ActiveX controls, it's been a constant drain on Microsoft profits. So, he'd love to drop it and take us back to those days when application development was directly tied to the OS.

It's really hard to believe Bill wouldn't be bothered by Pop-Up ads just like the rest of us. Or, is every popup a penny in his pocket?

Win95/98/ME: Bill would have personally strangled the ME team had he had to use that crap. So, we can be sure Bill was always an NT guy. Still, it's hard to believe Bill sat down for long in front of the clown colors of Windows XP. Again, lending credence to the theory Bill doesn't turn on his own machine, much to our detriment.

In Summary: Bill uses Outlook.

Steve uses Mail, IPhoto, ITunes, Safari, Calendar, Address Book, Graphics Converter, Quick time, Stickies and OmniGraph( OmniGraffle ) on a regular basis. These app's are written to a higher standard then their Windows counterparts. However, Steve doesn't have Feature-itis. These app's aren't laden with buggy, untested features.

Calc: Steve doesn't use the calculator. Or, he uses it with paper-tape and voice on. Otherwise, he'd notice it doesn't appear on screen without the paper-tape option checked.

Keynote: Apple's replacement for Power Point. Anyone who's attempted middle to large projects in Power Point knows why Steve would want his own version. Life is too short to depend on Microsoft.

Java: Steve is a user of Java software. He's given Java a beautiful face, and increased its graphics performance on his platform.

FileMaker: Steve likes his own Database company. Although he's not a Java programmer or he'd have burned the ass of the guy responsible for the JDBC driver available for Windows to get the port of the driver for OS X. Where is it? We're still waiting? What could take so long??? ( OpenBase is a good alternative. )
Update: FileMaker has actually released version 2 of it's JDBC driver. I'm surprised a note didn't appear on Apple's Hot News section.

OS X: Steve uses the whole of OS X. Steve is worried about security, and has implemented stricter standards in the OS. Steve likes to look at a pretty face, the beautiful blue graphical user interface of OS X. Steve does cruise the internet wirelessly: AirPort and the Safari browser, with regular enhancements for security.

Finder: Steve likes to actually find things on his machine with Finder's 3 views of your data: Icon, Detail and ( folder tier? ) view.

Finally: AppleWorks: Steve may use AppleWorks for writing long memo's or chapters. But, he's got better eyes than I do. AppleWorks is highly stable, but its font size is a bit small for my taste. Increasing the font size reduces the number of words on a page. Microsoft Word for Mac's solution is better here, increase the page magnification. Update: IPage has been released. This is a simple page-layout / word processor program. And may fulfill many user's needs.

Microsoft Office for Mac: Beautiful interface / fragile program. The definition of a Microsoft product. Steve may use Excel. Bill should consider re-writing it in an Object Oriented methodology. Clearly, C isn't up to the task of handling such a complex program.

In Summary: Steve uses almost everything and is a lover of simplicity and stability. Application interfaces are honed down to a simple elegance. The most common tasks are analyzed and optimized. The fastest working approach for most work flows is improved. But, not a shortcut key for every feature, which would lead to clutter. When he's writing a letter or building a presentation he wants his mind on the subject matter. Not on constant worry that a fragile OS or application, or virus may eat his work at any second. The Apple environment is the most stress free environment on the planet. This may account for Mac users pledging death allegiance to Apple.