Looks like you can stack the federal & California First Time Home Buyer Credit

Based on FTB's clarification on how the new California First Time Home buyer credit works, it looks like you can get both the federal 1st time home buyer credit of $8000 and the California 1st time home buyer credit of maximum $10,000 (over 3 years).

The federal credit requires that you get into contract by April 30, 2010 and the California credit requires that you close on or after May 1, 2010 and submit your closing HUD-1 within 2 weeks of closing the purchase.