The PS3 may have a little more horse power than the 360 but they are both VERY powerful machines. The 360 and PS3 are already at a level that if one has a couple more gigagazopoes an terazetasuper drives than the other, it wont make anything look that much different.
Playing with the PS3 at E3 I can tell you, graphically It looks no different then the 360. Now granted we weren't physically playing on PS3's but the PS3 dev kits but again once systems get that high up in hardware power, a little more of something really makes no difference, they both look the same.
The 360 will have its killer app games that look absolutely amazing( Gears of War, Halo 3, Too Human) and so will the PS3( Metal Gear Solid 4, Devil May Cry 4, Assasins Creed) and they both will also have the blah average games. Its all in what type of fan and gamer you are.
And to second that, at E3 the PS3 not only didnt impress me but didn't really impress anyone. So to add a little fire to the debate, I will pass a PS3 and keep my 360 and get a Wii.