I may put the last two bits of this in as one diary on Friday. Thoughts?
--The State Legislature--
Normally, states redraw the district lines every ten years, after the census; even if they don't have to add or eliminate a seat, the legislature still needs to make sure that each district has the same population as closely as they can make it, and if partisan control of the chambers and governorship is different from the way it was the last time they did it, the new majority party will almost certainly be flexing its muscles and putting multiple incumbents of the other party either in the same district or in unwinnable districts.
This doesn't always work that way, or even very well, of course. In 1993, the Virginia legislature, with the same Democratic majority it had held since the party was founded, eliminated George Allen's seat; Allen had planned to run for governor that year anyway, and he won.
Since state legislatures are established by, well, the states, there is no definitive standard. 49 of them have an upper and lower house - Nebraska abolished its Senate during the Great Depression, partially to save money, and decided not to bring it back afterwards. Nebraska's one house is nonpartisan; obviously people informally belong to parties, but more often they group themselves according to their position on a certain bill at that time, so coalitions are fairly fluid, though there is largely a comfortable majority of conservatives in charge of leadership and administration. The upper house is smaller than the lower, usually by a factor of at least two, but apart from that nearly everything is different.
The Speaker of Maine's House of Representatives was Hannah Pingree (since Maine has term limits for its legislators, she held that position until the end of 2010, at which point she had to take a break before running for another four terms - with luck, when she returns, she'll be able to help retake that majority), who helped raise money for her mother's hugely unsuccessful race against Olympia Snowe in 2006. After Tom Allen vacated his seat in the House to have a similarly unsuccessful run against Susan Collins, Chellie Pingree took it.
Twenty-one state legislatures are controlled entirely by Republicans (though in a few cases the Lt. Gov. is a Democrat, which occasionally makes a difference, especially if the Senate is very closely divided), and eleven are controlled entirely by Democrats. The remainder are more or less evenly split, with half having both houses controlled by one party and the governor of another and the other half having the governor and one house of one party and the other house of the other. Rhode Island and Alaska are special cases: Rhode Island has Independent, formerly Republican, Governor Lincoln Chafee, who was the most liberal of the three candidates in the 2010 race, and an overwhelmingly Democratic legislature; Alaska has a fairly mainstream Republican Governor Sean Parnell, elected in his own right in 2010, and a House controlled by 24 Republicans and 4 Democrats to 12 Democrats, and a Senate controlled by 10 Democrats and 6 Republicans to 4 Republicans. Weird as hell, huh?
The split legislatures are also even, in that half of them have Republican upper houses and half have Republican lower houses - not counting Alaska in either category here, nor the evenly split Oregon House, with co-speakers and co-speakers pro tempore. Surprising that newly-returned Governor Kitzhaber, who presided over a Republican legislature from 1995 to 2003, hasn't tried appointing one of the Republican representatives from a swing district to some post in his administration, to try to take his seat, and thus control of the chamber. Then again, perhaps he has, and they turned him down.