Including blocking out online play for weeks at a time and distributing your personal information to hackers :P. I kid in part as PS3 does have some fantastic games. For my money though, you simply can not beat Xbox Live for online play. I would recommend a 360 over PS3 every time unless you are only getting a PS3 to play its unique titles, like I did when I bought mine.
OT: Frankly, get both. Get 360 for sure because it is likely going to last at least another three years with third parties continuing to produce games for it. Once more info comes out on the Wii and its games lineup you can decide to invest in it or not. I'll believe Nintendo is moving away from their once wildly successful family strategy when I see it. They made a boatload of cash with that strategy on the Wii but it has completely killed their continuing sales. I'd like to see how the new system is designed as a movement oriented system or a controller oriented system. I want to know about these new controllers that are going to have what are assuredly useless screens that massively drive up the cost of a remote. I want to know what they are doing to expand online play which will come if they actually have mature titles like FPS games.
You can't go wrong getting an Xbox now especially with the ridiculous line up of upcoming titles like ME3 and LA Noire. You could go horribly, horribly wrong investing in a system that is being released mid-console cycle for the other two companies which could seriously limit the amount of intellectual property released for it that isn't just Nintendo owned trademarks.