All of the UC's have online status check pages. Irvine ijndicates rejection on their status page followed by a letter. For UCLA, if it indicates a final decision letter is sent before interview, then you are rejected. UC Davis is the most efficient school - they reject through email, but they also do everythign else through email, just to be fair. UCSF rejects through snail mail following update on status page. UCSD, I am still on their alternates list so no idea how they reject.
be patient, the UC's are notorious for being slow and it's still pretty early! don't give up too soon, although i know how you feel as i am waiting as well... for now, i just tell myself no news is good news!
I haven't even received acknowledgement of receipt of my AMCAS application from the UCs. All schools except for the UCs, Duke, and Vandy have responded to me, grrr.. damn you UCs...