I own both machines. The Xbox has better online play but is $50/year so you better use it often to get your moneys worth. If you're an occasional gamer like me its not worth it. The Xbox is a better media player, I find it plays more files than the PS3 does, it streams the video podcasts that I download on my pc beautifully, it also has a Netflix player built in now if you pay the $50/year for online play. The games are still better on the 360 although the gap is narrowing. Forza is a great game on the 360 however M$ wont get their head out of their ass and allow the high end wheels like the G25 to work with it. The Microsoft wheel is pretty nicely designed but totally lacking in build quality which makes it totally abysmal to actually use, it feels like a toy. I did have to have the warranty service performed on my 360, it took exactly 7 days round trip, cost me nothing, even packaging was included, and I got a free month of online play for my trouble.
The PS3 is a great blu-ray player. Its fast and has all the special features enabled. It works with the G25 wheel as well as the DFP and others that are a joy to use. I actually traded in a few of my 360 driving games for the PS3 versions just so I could use the better wheel. Online play is free but not as nice to use as the 360. It plays some media but seems more picky than the 360 the streaming functionality is not as nice either.