In the wake of NY-23 last fall a lot of Democrats hoped that the ideological war within the Republican Party would impede GOP progress in 2010. I just don't see it though.
Take a look at Florida- yesterday's Quinnipiac poll showed Marco Rubio getting 82% of the GOP vote against Kendrick Meek and Charlie Crist getting 80%. The Rubio people might be disappointed if Crist still manages to win the primary, but they'd still vote for him to keep Democrats from increasing their margin in the Senate. And the Crist people might think Rubio is too far to the right, but that would probably be outweighed by a feeling that Meek is too far to the left.
In either case Democrats are less unified. Meek gets 77% of the Democratic vote against Rubio and 69% against Crist. In 2008 there was no unity gap in Florida with both Barack Obama and John McCain getting 87% of the vote from their party.
You could try to chalk that up to Meek's low name recognition in comparison to Rubio and Crist but there's no gap in the number of undecideds between the Democrats and Republicans in Florida.
In Massachusetts, New Jersey, and Virginia Republican voters have been more unified than the Democrats. Whatever ideological differences they may have within their party pale in comparison to their common hatred of President Obama and Congressional Democrats, and while the disunity story will probably still get a lot of press I don't think it will ultimately have much of an effect on what happens in November.