As I write, the polls have closed in Virginia, but no result has been announced in the governor's race. New Jersey's polls will close soon.
This election's significance can easily be overestimated; only a few states have meaningful contests, and low turnout will be the rule in all.
Virginia is a state with a solid 30% or so of Democrats, primarily in the D.C. suburbs and Tidewater area, and a solid 40% of so of Republicans. Republicans have a slight edge, but races are determined by a swing group of moderately conservative voters with loose party affiliations, if any. Virginia laws don't allow governors to run for re-election, so there is an unusual effect in which the swing vote punishes the incumbent's party if they don't like the state of affairs, an anti-incumbent effect which doesn't punish the incumbent (who can't run).
New Jersey is a state which normally votes Democratic, but politics there have been conditioned by a massive corruption problem for local politicians, primarily Democrats. Incumbent governor Jon Corzine is a rich banker, so resentment about the bank bailout may also work against him; countering that is an enormous advantage in spending for Corzine. This will probably be the race that will remain undetermined late into the evening.
The third race being closely watched is a special election in New York's 23rd Congressional District, from which the moderate Republican Congressman left to become Secretary of the Army for the Obama administration. The moderate Republican woman who had been nominated by the local party machinery was lagging badly behind a candidate from the Conservative Party (which has a long history of providing a check on tendencies of some Republican candidates to drift too far from the right wing). She dropped out last weekend and recommended her supporters vote for the Democrat (!)
The immediate result was a large increase in undecided voters and a small bump for the Conservative, probably among those who hadn't been able to decide between the Republican and Conservative when both were in the race.
There are some other races, like the mayoral race in New York City, where Michael Bloomberg is expected to win easily a third term.