In fact, since I'm lucky enough to have my own company, I dictate what we use. I have a fulltime freelancer that brought in his PC against my better judgement. After god knows how many headaches and lost funds, I finally convinced him to just buy a damn Mac. Sure enough, he has eventually conceded that he prefers the Mac, but must have his killer home PC for games. How many times have we heard that?! We still have the PC for certain specific things, but I hope even that will end with X (though I guess we'll still need one for testing,etc.).
As a founder of the company and 'the IT guy', I decide what computers we use. Then again all three co-founders are Macintosh fanatics, too. But we have one Linux/Intel server for website staging and file server and a Windows XP box for testing purposes. All other computers are Macs. For we're in the business of Communication Concepts & Visual Communication.
I'm a partner in a design company and made every use OSX when it came out (well from 10.0.4). This was a great move 'cause we don't have to learn a new OS anymore and 10.1 gives us that speed! (And Photoshop works just as well in Classic).
I work for a major telco company doing webdesign, and we're forced to use WinNT 4.0 machines. Thankfully, I get to telecommute every other day, and my home setup is 3 Macs and a PC, so I'm not completely shafted...