Alright...
Even though comparing OSX Leopard to 7 is unfair, (you should compare Snow Leopard), I'll do it for the sake of answering the argument of the two.
Windows 7 DOES have superior Windows management. I concur. Unless you're extremely good with Mac Expose, you have to agree that window 7's jumplists and aero snap is quite useful. In mac, I can get expose to show desktop immediately, and I can get it to show all my windows, but window 7's jumplists implementation is extremely nice.
This said, Windows 7 beta, at least for me, CANNOT run everything well. Explorer 8 has some bugs and some games fail to run on it. Also, windows 7, other than an improved UI, has pretty much nothing except for libraries in explorer that is different from Vista (at least for my usages). Therefore, every argument against Vista almost works against 7. The backup in OSX is much more nifty, the system is much more stable. Mainly, OSX has better software as well, most third party software in OSX is much more streamlined that third party software in Windows.
Basically, I could see you using just Windows if you're a person who surfs the web, writes basic documents, or runs Windows-only applications. Otherwise, OSX does have awesome things such as iLife, Spaces, the backup utility, iWork...