To be honest, I was asking the same question.
I quickly discovered though you can't really do a straight up comparison between ps3/wii.
All the effort on the wii has been put into the movement functions. The actual games & software are secondary to this. Hence all the games I've seen so far on a wii have been dodgy looking "cartoon" graphics.
Even their flagship "wii sports" hasn't got enough space to have figures running about the screen with legs, they just hover around the screen.
As has been said already, the wii is a social console. But if you played it by yourself, it would bore you within the hour. The software is aimed purely at this level so you will never get the breathtaking graphics you get on a ps3.
The Ps3 on the other hand ( yes jamie i'm a sony gaydo

) can be both. you have the motion sense controllers & you have the network play/ 2 player setups. But you also have the "bloody hell" graphics of the software & the sheer versatility of the console. When you buy a ps3 game, the first time you play it, it updates to the most recent software version to repair known glitches etc.
Plus a little known fact is that a dual layer dvd has about 7-8 GB on it. A Ps3 blueray disc has about 60GB on it.
Go sony m8, you know ya wanna

PS
Ask any ps3 owner about the joy of Call of duty 4 online. Its playing soldiers for grown ups - well big kids anyway
