The Republicans will keep the House no matter what.
There have been, since the ratification of the 17th Amendment, 20 flips of a chamber of Congress by a vote of the people. 17 of them happened when the incumbent President was the same party as the party that controlled the incumbent chamber. One was a result of both a weird muddle (the 2000 election) followed by a wartime rally effect in the next election (2002). Two happened in 1948, which was a strange election (that was the "Dewey Defeats Truman" year).
So, since a Democrat will be President in 2012, the House will remain Republican.
See, if people think things are going well, they vote for incumbents. (See Clinton in '96, and how the Republicans retained Congress, or see Reagan in '84, and how the Democrats retained the House.) If they think things are going poorly, people will vote against the President's party (see 2008 or 1992, where the party of the incumbent president lost the presidency but the incumbent opposite-party Congress stayed in power). Since the Republicans are both the House incumbents and not the president's party, they're in good shape for 2012.
Throw in that a bunch of state legislatures went GOP, while California handed over Congressional redistricting to an independent commission, and the post-Census 2012 districts are going to generally be more favorable for Republicans.