This surprised me a little:
How much does the progressive mesh differ from the original PS2 R&C-engine in terms of scale?
Al Hastings, Chief Technical Officer: Our level-of-detail techniques are actually much simpler on PS3 than they were on PS2. We made the decision to steer away from doing heavy amounts of geometry processing on the SPUs, so instead we’ve focused on techniques that can be implemented directly on the graphics chip. There are a lot of trade-offs with this approach, but ultimately we like the fact that it gives us more flexibility in our engine and it frees up the SPUs for gameplay related processing.