I used Win7 for 18 months before switching (back[1]) to OSX.
I'd echo what most people have said. Win7 and OSX 10 are pretty much on a par in terms of stability, and the security thing is definitely overblown: in 12 years of using several Windows variants, I've never had a virus.
Feature-wise, I'd say they are too close to call. Windows has a few edges on OSX, OSX has a few on Windows.
OSX wins for me in a few areas. First, there are far, far fewer OS updates. On Windows, I'd have to restart my machine maybe once a week for updates; on OSX, it seems rare.
Second, start-up and resume times. If I do have to restart OSX, it's about twice as fast as Win7, and resume is almost instant (versus 15-ish seconds for Windows). It's also much easier in OSX to auto-start the apps I want and nothing else (you can do the same in Windows, but it's a lot fiddlier).
Third, Time Machine. For a laptop user, TM and Windows Backup are night and day. TM is far, far easier and slicker.
Fourth, migration. Switching to a new machine and carrying across all your old apps and settings, OSX is again far easier and does a much better job of it.
My main gripe with OSX is the way it actively tries to hide the file system. Yes, I'm sold on letting apps manage it as much as possible (despite being deeply resistant to the idea initially), but there are times when I want a particular file in a particular folder because my folder structure (used for years under Windows) mirrors my business structure, and I sometimes have to battle OSX to achieve that.
Overall? I don't see a massive reason to choose one over the other, but having made the switch to OSX for circumstantial reasons, I do have maybe a 20% preference for OSX.
[1] I used Macs from 1984 to 1999, so a switch back to Mac rather than to OSX!