It's not as cut and dry as they'd like to make you think it is, but for gaming the 360 is more powerful than the PS3. Without getting into the technical details, it has a slight fill rate advantage, a slight memory advantage (more flexible architecture, less OS overhead), and a signficiant general purpose CPU advantage.
As we get into later generation games, it should become more and more obvious that the 360 is more powerful than the PS3 -- developers will be using libraries which will take better advantage of additional threads as well as having a growing and improving multithreaded codebase. This will benefit the 360 much more than the PS3 due to the 360 having 3x as many general purpose hardware threads.
The PS3, of course, will see some improvement as well but I'm saying that the gap between the 360 and PS3 will grow due to the hardware disparity. The biggest disparity -- the extra PPC970 CPUs -- is the hardest to optimize for. The SPUs on the cell just aren't suited well toward gaming. You can't improve libraries to use more single precision floating point calculations if you simply don't need them done, and they're not a substitute for general purpose CPU power.
