People got so sick of Bill Clinton that they re-elected him in 96 by even wider margins.
Clinton's win in 1996 did nothing for the Democrats. In fact it may have even hurt them. He governed pretty much as a Republican in his second term and kept Democrats from retaking the House in 1998. Remember, if Democrats have a bad 2010, they will likely be shut out of the House until 2022 because Republicans will control gerrymandering.
Gerrymandering will be more pro-Democratic since any time since 1980 simply because they control the DOJ which has to approve the maps of most of the states the Republicans could conceivably screw them in(ie. every southern state, plus they can veto maps in OH, MI, PA, and FL that screw with minorities). Since 1990 the DOJ has been incredibly aggressive and arguably had more to do with the Republican House gains in 1994 than any GOP legislator.
At the same time, the Democrats have a good shot at controlling California completely and wiping out as many as six GOP seats.
I think a good year is not necessary for the Democrats, but a bad year would doom the GOP at least until 2022.