The big pre-debate news in WH 2012 is that Chris Christie has endorsed Mitt Romney.
The general political science position on these type of endorsements (high-profile elected official) is that they are in general a sign of party commitment to a candidate. The complexity behind it is that governors are both party actors and, at the same time, individual political actors with their own preferences and self-interest that may or may not be connected to their party. What that means is that in practice, it's impossible to tell if a single endorsement is an indication of broader party support or not. What you want to look for is the overall pattern of endorsements...but then again, that does include noticing individual endorsements. Got it?
It's also the case that parties in basic agreement need to find a way of coordinating their actions in an environment in which the rules of the game make coordinating difficult -- but parties may also include areas of basic disagreement, and so from the outside it's hard to tell whether a particular endorsement -- or even a set of endorsements -- is part of a party-wide coordination effort or party of coordination within various factions (or groups) that are fighting over the nomination.
And there's more! If there are competing groups, the loser may simply accept defeat (look, the bulk of the party has decided where they want to go; we might as well go there too) or the loser has the option of taking it to the voters in the string of primaries and caucuses.
Meanwhile, that's all about party actors. There are also, of course, presidential candidates, and they are competing to win the support of all these folks -- and they also have the choice of whether to accept defeat or not. The two things are linked, but they aren't identical. Some party actors will have no candidate who really represents their group; some candidates may, either because of media backing or other independent resources, be able to keep a campaign going for some time even without the support of many party actors at all -- although since 1976, no one like that has ever come close to actually winning a nomination.
Once we get to the primaries and caucuses, we can expect that voters will generally follow the lead of coordinated party actors. But not fully, and not always. Voters may, regardless of other cues they're receiving, flock to a candidate they like or avoid a candidate they don't like (indeed, I've speculated that the latter was what happened to Howard Dean in 2004). And then there's also other influences on voters, including independent actions by the news media (that is, other than media actions which follow norms that re-enforce cues from party actors).
So a big-name endorsement is overall worth paying attention to. Actually, Mark Halperin of all people gets this fairly close to correct: "Voters don't care much about endorsements, but, for the donor community, other governors, and the Christie-loving media, this is as good a get as exists in the party today." It's a legitimately good grab for Romney, although it's hard to tell right now whether it will turn out to be party of a real pattern or not.