Obama was actually ahead in Iowa polls prior to the caucus. I think Mayor Pete certainly has a good shot of winning, but Obama winning Iowa wasn't that much of a surprise. The big surprise was Clinton coming in third, something Biden could very well replicate.
it was a more mixed bag. Clinton still led in some polls even right before caucus day, and very few polls gave Obama a lead close to his ultimate margin, which came as a surprise. In November, he was not leading but instead was roughly tied with Edwards for second.
https://en.wikipedia.org/wiki/Statewide_opinion_polling_for_the_January_2008_Democratic_Party_presidential_primaries#IowaDiscounting ARG (lol), Zogby (lol), Research 2000 (proven to have been faking) and Strategic Vision (proven to have been faking) (NB: 2008 was a polling wasteland), the polls conducted after Christmas had:
Des Moines Register: Obama+7 over Clinton
CNN: Clinton+2 over Obama
Insider Advantage: Clinton+1 over Edwards with Obama in a distant third
MSNBC/Mason-Dixon: Edwards+1 over Clinton with Obama one point further back; with second preferences, it was Edwards+7 over both Clinton and Obama.