well, you get what you pay for as far as online play is concerned. xbox live, albeit it costs money ($50/yr) has much better features, and they're more streamlined. the playstation trophies were/are such a joke. Look at the guide for the xbox (friendslist, messaging, recent players, voice chat) all accessible at any time. There's no need to go back to the dashboard (xmb on playstation) to do any of that.
Also, they stripped the backwards compatibility with all but the 80gb version of the console, as well as other features that i cannot think of atm since launch. I'm not saying that xbox's backwards compatibility
is the greatest (cause they use a software emulator), but their list is improving.
Also, as far as games go, I don't really see any reason for me to buy a ps3 for games, since I've got the xbox already. Also, take a look at a couple of games for both the xbox and the ps3, such as the orange box. The framerate on the ps3 is so horrid and choppy. The game got over a 9.0 review on gamespot, but was nowhere near that on the ps3. Tom Clancy's Rainbow Six has no following, and bad support on the ps3, whereas the xbox again, one of the top rated games. Aside from a few exclusives, such as metal gear solid, little big planet, and grand turismo (hey, i've got forza), there's not much that's impressive).
I don't know how the marketplace/store's compare to each other, as I have not personally used the playstation store, but my friend has it.
Also, don't forget that there's an update on Nov 19
for any xbox user. a new dashboard and the ability to stream over 120000 movies from netflix.
w/e, that's all i'm gonna say. i'm not gonna get into hardware specs, as games and features matter more for me than how powerful it is.