I think all the evidence we need that it is time for the next gen to roll around is how bad load times are getting. Bigger open games like Fallout and Bioshock have always given us load screens lasting in the double digits of seconds, but I've always been pretty accepting about that.
However, the load times in Fallout: New Vegas are so amazingly ridiculous, sometimes lasting minutes, even after being installed to the hard drive, it makes it really hard not to feel like the ambition of this game far exceeded the abilities of five year old consoles. Portal 2 load times are also pretty painful.
As much as I don't want to spend money on a new console anytime soon, especially since I am not an early adopter and it would mean years of not playing the newest games, I think it is past time for the next gen to begin.