In 2008, Barack Obama won California 61%-37%, a remarkable performance above what any California Democrat could do statewide. If we use the same 98% the Presidential race got in 2008 the average statewide race is 54% Democratic 44% Republican. The typical Democrat would win by around 10 points. Barack Obama's 13.75% lead in the average of the last four polls tells us that Mittmentum isn't nearly as strong here as it'd appears to be and that Obama is still doing very well.
One piece of conventional wisdom is that because the President will win California he'll dominate the congressional districts. While he will dominate very Democratic districts, he won't dominate the swing districts.
Using the 2010 senate race as a guide the percentages below would be about what you'd expect in a race where the Democrat wins by 13.75%.
I project Mitt Romney will win 5 competitive districts, Barack Obama 3, and 4 will be roughly even. The President will win CA-9, 41, and 47, Jerry McNerney's district and two open Southern California districts. Barack Obama's coat tails might be enough to bring those home.
Mitt Romney may have coat tails too. Four of the five congressional districts I project him to win are occupied by Republican incumbents. Democrats failed to win any of the 8 Republican congressional districts that Barack Obama won in 2008. If they couldn't unseat Republican incumbents when Barack Obama won the district their chances should be less when he loses it.
The four districts that project to be roughly even have three Democratic incumbents. Since incumbents usually beat their Presidential candidate, John Garamendi, Lois Capps, and Jim Costa should be favored to win. The last district, CA-26, is an open district contested by Republican Tony Strickland and Democrat Julia Brownley. There appears to be no favorite there.