Right now, it seems to me that the 360 is about as good as it's going to get.
The PS3 is under-achieving because people would rather stick to the tried, tested and familiar paths of the 360 rather than taking a risk and actually using the PS3 to its full potential. I realise some of you are too young / stupid to remember this, but EVERY SINGLE CONSOLE goes through the same pattern. Every single one.
Pick any console, and compare the first generation of games to the last. You will see notable improvements.
Let's take as an example, and I'm already wanting to stab myself in the face for doing it, Tomb Raider. Mechanically speaking, Chronicles (that was the last PSX one I think) is FAR better than the original. In theory, there's no reason they couldn't have started with Chronicles-level quality, but they didn't. Why should they? No sense investing bucketloads into a game that might not pay off. Instead, it's better to use 20% of the system, then 25% in the sequel, then jump to 35% because a competing game came out that used 30%...
The point is it will take time for the PS3 to really start to shine.