Is it me or it would be really stupid to sell your 360 to buy a PS3? Especially if you want one for the multimedia capabilities and exclusive games. How about just buying a PS3 and GT5/GoW3 or whatever exclusive games you're interested in? That way, you don't need to buy your multi-platform games more than once... Unless you somehow manage to get someone to buy your 360/games at a good price.
How many cups of darkness have I drank over the years? Even I don't know...