Not sure... they're going to boost the level-1 cache by a factor of four, from what I'm reading, and the level-2 cache to 1Mb. As I understand it, the long pipeline of the P4 causes a big penalty if the CPU guesses a branch wrong and has to start from the top, so they are evidently working on improving the branch prediction too. Hope I'm not butchering that too badly. Anyway, its strongest point might be that Intel is hoping to eventually squeeze 5 to 6 GHz out of the new core, which is .09-micron technology.
Regarding the socket question, I've found conflicting reports. The Register says 479 pins
here but another place showed socket478. Intel probably knows but they historically don't talk about unannounced products. I speculate that you should not expect today's motherboards to support Prescot, even if it ends up using Socket478, because it will probably be designed with a faster type of memory in mind... DDR-II maybe? It reportedly runs on a 666MHz fsb.
Any Intel cogniscenti have more info on this question?
edit: I know Prescot is somewhat tangential to your actual question about forward compatibility,
Armageddon415, but if you can sift the facts out from the rumors (and rhetoric), there may be some relevant info
here. What will your most intensive usage be, anyway... that might be a relevant question if you're shopping for the right platform for your needs?