Yeah it's very different. And, if you ever need windows again, you can dual boot. Thats what I do. Windows 7 for games, mac os for everything else, and for my blizz games.
A dozen personal systems, 10 Windows 7 devices of various types, 2 Windows 2008 R2 servers. Three work provided devices, two laptops and a desktop running XP.
13" MBA as my primary system
Windows 7 desktop used to be my main primary system but now it's just a glorified torrent/storage computer until I get a NAS to transfer everything over.
I'm a recent convert to OSX with my MBP purchase. It's my main dev machine now, even for Flash stuff which is a bit ironic I suppose. I still use my main Win7 rig, but mostly just for VS2K10 and Starcraft 2. I'll be moving to an iMac with bootcamp later this year and turning the Win7 rig into a vmware box.
My desktop is win 7, my server is server 08 r2, and my mbp is os x obviously; I use the desktop mainly, the server is touched damn near never (it's up and running so why mess with it.) and my MBP is for school and coding and stuff.
Usage wise it's about a 70 windows/30 os x percent split; I prefer OS X but I don't have the means to make it my main OS right now and I have this mod bug that bites me every now and then and a Mac won't let me scratch that itch unfortunately, I came so close to hawking it all for a 27" iMac but I couldn't bring myself to do it in the end.