Election Verification Exit Polls were conducted on November 4, 2008, in the 25 most populated counties in California, which included 10 polling sites in Los Angeles County representing 19 precincts.
The difference between the official results and those of the poll were 5.74%. Given that 24.23% of California voters are in LA County, that translates to 11.48% of total votes, more than enough to set ring alarms set at the standard "4% +/- margin of error." EDA co-founders Sally Castleman and Jonathan Simon write discreetly that "It is beyond the scope of this study to know if any corruption was due to honest error or intentional fraud," but also say that based on their numbers, "Further investigation is warranted."
For more detailed analysis, read the EDA's paper.