As of 11:21 p.m. ET, and with 92% of precincts reporting, Mitt Romney has a 13-vote edge over Rick Santorum.
Romney has 27,830 votes, Santorum 27,817 votes.
There are currently two counties that have made no reports at all: Madison in central Iowa, and Monona in western Iowa. Santorum has been carrying the west, while both Santorum and Romney have done well in the middle. However, neither of those trends are necessarily predictive for the still-absent counties.