When the votes start coming in, it's important to remember that the US Presidential Election is not win by the popular vote but by a system called the Electoral College which awards states 1 vote for every seat which they have in the Congress (both houses included). Although states are free to award Electoral College votes with whatever method they like, the vast majority award them on a winner takes all basis.
To take office, a candidate needs 270 of the 538 Electoral College votes and because most states are awarded as chunks, candidates tend to work hardest in those states most likely to swing for them and ignore the states which are safe either for or against them.
For this reason, California has been assumed to be Democrat and neither Romney nor Obama have really paid it that much attention despite it being worth 55 of 538 Electoral College votes; because California is a prize worth 10% of total vote, perhaps more attention should have been paid to it. I think that there is a fair chance that California may flip to being a Republican state and with it, the Presidency would go to Romney.
As it stands, California has 34 Democrat and 19 Republican House Delegates and both of its Senators are Democrats as is the Governor. Preliminary polls have shown that Obama has been typically polling in the low 50s whilst Romney is in the high 30s. However, when picking a president, the rules of the game change considerably.
In 2008 Obama was able to mobilise a great many people who otherwise would not have bothered to vote at all. 2012 is different to 2008 in that with the Global Financial Crisis and meddling by the Congress, Obama's Presidency simply hasn't been able to deliver what he promised. Since a great deal of people are politically illiterate, it's easy to blame the President for the machinations of Congress than anything else.
Obama is likely to lose ground in south Los Angeles right down the two spines of the I-110 and I-710. Places like Alameda, Lynwood, Compton, Carson, Long Beach and Lakewood are going to be far redder than they were four years ago. The San Bernadino Valley from Pomona and eastwards along I-10 could be another strip in LA which is likely to flip to red.
San Francisco ever since about 1992 has been staunchly blue but I suspect that apathy in this election combined with a more local advert campaign, is likely to see a greater turnout of Republican voters. The other big patch of increased Republican turnout will be in San Diego. San Diego is the eighth largest city in the United States and although it has a very large proportion of immigrants from Mexico, with Mexico being just across the border, those areas surprisingly are showing a greater Republican preference than they have in the past.
I found it curious that this year there was an unofficial event called "Pulpit Freedom Sunday" in which 1,477 pastors signed up to preach on politics, in defiance of a 1954 law preventing charitable groups from making candidate endorsements but this year, the IRS officially announced its ambivalence.
San Diego in particular and California generally, has the greatest numbers of pastors who signed up for this, and although they didn't explicitly suggest that people vote for Romney, it was another avenue of encouragement.
I think that California is the sleeping giant in the 2012 Election and that come Wednesday, it won't be so much the smaller battleground states which will actually make the difference but the big 55 jobby that everyone forgot about and neglected.
Watch closely for where the red eats into the blue in California. In 2008 the difference was 8.2m Obama vs 5.0m McCain. 2012 in my opinion is likely to be 6.1m Obama and 6.1m Romney (which is a smaller overall turnout than 2008). I honestly think that the final margin in California will be less than 10,000 votes, will more than likely be challenged and for the first time since 1988 when George HW Bush thumped Dukakis 426-111, Romney will win but only just by 275-263. If Romney doesn't win California then I think that the results with show Obama winning 318-220.
This is from PBS. Have a go, it's fun: