The Xbox 360 is somewhat more powerful but only because it has twice the RAM and a better memory bus and controller architecture that achieves higher data throughput.
The 360 also has a slightly better GPU as well. The PS3's graphics controller is just below a GeForce 7800.
Still, the graphics capability of the PS3 is virtually identical to the Xbox 360 with only a marginal drop in FPS on the PS3.
While the PS3 is slightly less powerful and doesn't have Halo 3, it does play BluRay movies, have a very high reliability record, a free Interweb browser, free online multiplayer service, and of course is a completely unlocked system (minus the GPU).