I moved from windows NT to linux then to OSX, however I'm chained to an XP machine at work and run linux and OSX at home.
A few points from the experience of a typical user:
Microsoft Office runs like a pig on OS X, I learnt this the hard way writing a 18000 word dissertation in it. This is not the fault of the computer. I sincerely believe MS have written a turkey for the Mac. Be warned. However if you only write the occassional letter or essay you will have no problems. I use an Open Office variant instead.
My mac never crashes, however it does run hot (iMac g5). I am hearing much better things about the new intel macs. Despite this, my mac was last rebooted 117 days ago, due to a shortage of wall plugs and I needed to put the vac around!
Macs appear to have simple, underfeatured defualt software, however do not underestimate the power of apple scripting and automator, the built in automation software - you can so much more with a few iLife apps than you can with the microsoft equivalent (if there even are any).
If you want to exercise your ubergeek, you have no better opportunity in a commercial OS. OS X is derived from BSD Unix, and the terminal environment is fairly easy for a linux user to get to grips with. You also have access to the vast, unrivalled software base of linux through the various porting initiatives. This is leagues ahead of the freeware and shareware base available for windows, I assure you.
Networking? Plug and play. Perhaps a bit too easy. However unlike other operating systems OS x ships with sensible defaults and is fairly secure from the outset. A few configuration screens later and it's pretty darn bulletproof. Yes I am complacent!
File compatibilty with Windows? Never been an issue for typical home/office use.
Not found a graphics or audio or video file I couldn't open or convert.
Do I feel the need to use windows or anything? No. At work I find myself missing features from OS X, but never the other way round.
Gaming: you are out of luck if you are seriously into gaming and own a mac. There's a few big name titles like Uneal tourney and quake available. Goodd luck finding a game store which carries mac software. Head online for a better shopping experience. Buy a console instead.
Would I go back to linux or windows? Linux - perhaps, Windows? Never.