Desirable possibility A:
Republicans take control of House and Senate.
Democrats realize Obama is a liability and run a moderate candidate in 2012.
Unnamed Democrat wins the election, keeping the Legislative and Executive branches at odds.

Desirable possibility B:
Republicans take one chamber of the Congress and nearly take the other, leaving Democrats scared in one and disempowered in the other.
The Democrats stick with their incumbent in 2012.
The Republicans fuck up less than usual and win the 2012 election, but still end up without control of both branches.

Scale of Desirability:
A---*---------B

Scale of Likelihood:
A---------*---B

Given fulfilled prerequisites in 2010, potential for disastrous unilateral control in 2012:
A*------------B

Conclusion:
All things considered, Tuesday's results are close to ideal.