Polls and Primaries
Chris Bowers at OpenLeft has a very useful post up analyzing the various factors that might boost and limit post-IA/NH "bounces" in national polls for presidential candidates in 2008. Be sure to follow the link to Mark Blumenthal's more general discussion at pollster.com of the relevance of primary polling.
It's worth remembering as an additional note that advance polling in the one "unbounceable" state, Iowa, is notoriously difficult, since it's hard to really establish an accurate "screen" for likely caucus-goers. Iowa's complex caucus rules, which can produce results significantly out of line with statewide opinion, present another problem for pollsters.