I posted most of this in another thread, but I don't mind posting it here again.
The Prescotts will have 1 meg of L2 cache (Northwood P-4's have 512k). That by itself should help performance. They will also have SSE3 instructions. How much this will help (if at all) has yet to be seen, but I suspect there should be some efficiency improvements with the SSE3 realization.
How well the Prescotts overclocks is yet to be seen. I'm assuming they'll follow a similar path as previous cores. For example the Northwood when it was first released two years ago was hard pressed to O/C any higher than 2.5 to 2.6 gig. As the core matured and improvements were made, the overclocks got better and better. Within 6 months people were beginning to hitting 3 gig on air. New steppings were released and the overclocks climbed higher.
My prediction is the Prescotts will do the same. The budget minded folks might be smart to take advantage of the cheaper Northwoods and let the Prescott core mature a little and prices to drop before jumping in. For those of us that are adventurous and can afford it and like being pioneers, we will be happy to test out these new Prescotts and see what they'll do.
Sounds like Intel will release the Prescott on Feb 2 and then will have price drops on Feb 15. So waiting a couple weeks might save you a few bucks if you plan on buying a Prescott. The other thing to consider is that the second generation of Prescotts will follow fairly soon and this brings a new chipset and socket to the table.