Personally, there isn't much between the 360 and the PS3 in my eyes. The 360 has got some corkers coming out for it too (Halo 3, Gears of War, Forza, Splinter Cell) aswell as hidden gems that always pop up. I dunno if it'll offer better games as most games come out on all platforms these days anyway, but the exclusives it has are generally on par (and usually better IMO) than the PS3s equivalents.
I can imagine Live will be alot better than the PS3s online service having been around a lot longer, but you never know what Sony will pull out of the bag.
What I'm saying is, in my opinion, there isn't enough difference between the two consoles regarding games and whatnot at the minute to warrent a £150 price difference. Take my comments with a pinch of salt though because obviously, the PS3 isn't out yet
Just my two cents