Big Picture
Democrats won six Governorships, and lost none, moving from a deficit of 28-22 to an advantage of 28-22. The gains came in Arkansas, Colorado, Maryland, Massachusetts, New York, and Ohio.

In state legislative bodies, Democrats control 56 chambers, Republicans control 40. Two, the Montana House (previously tied) and the Pennsylvania House (previously Republican controlled) are undecided. Democrats took nine legislative chambers, and lost none. The gains came in Indiana (House), Iowa (House and Senate), Michigan (House), Minnesota (House), New Hampshire (House and Senate), Oregon (House), and Wisconsin (Senate). The Iowa Senate was previously tied, and the Oklahoma Senate, previously controlled by Democrats, is also now tied. I believe, however, that the tie in the Oklahoma Senate goes to Democrats, because we have the Governorship there.

Democrats control 3,964 state legislature seats, and Republicans control 3,307. I do not know how many are controlled by third parties, or are currently undecided. Democrats also have a non-southern majority in state legislature seats for the first time in many years.

My favorite factoid in the state legislative world: there are 400 members in the New Hampshire House of Representatives (that's one representative for every 3090 residents, roughly). We picked up 89 seats in NH to give Dems the majority in the House for the first time since at least 1922.

Chris makes a number of critical points: we have "restocked our bench," with legions of new potential candidates being groomed for higher office; Dems can start to govern progressively in many states; these gains can be built upon for creating a much more Dem favorable redistricting after the 2010 census.

And here's a great advantage not mentioned by Chris: historically the party that controls the most governorships has the advantage in Presidential elections. If you want to think about it in terms of electoral votes, Democratic governors are in place in states that combined will have 295 electoral votes, up from 126.

Ah, the wisdom of a 50-state strategy.