vnacyd, my experience was a couple of years ago, so I don't know if it's still right: UCSF has a "high" and a "low" ranked waitlist, and they have never gotten down to the low one. They will tell you which you are on, so that can be worth knowing. Also, they take people off the high list up through the end of the first week of classes, and it seems like a lot happens as late as July. I know someone who didn't get in anywhere else but got a call on the Friday morning at the end of the first week, inviting him to join the class at anatomy lab that afternoon! (How can you get that far at UCSF and be rejected everywhere else? Sounds odd, I know--I think some personal connections were involved...)
There is a lot of action on the UCSD waitlist--several people I know got a call in August! They only give you 24 hours to decide, which I think is kind of mean.
UCD used rolling admissions and was really disorganized the year I applied. I don't know anyone who got off their waitlist that year. They won't tell you where you are ranked. Someone who works there told me their class was pretty much set by March, with very few changes after that. She wasn't sure they even bother to rank the waitlist.
UCLA is a mystery. They don't tell you anything, and I don't know anyone who got in off *their* waitlist, either. But I don't know much about them--I didn't apply there and I don't know many who did. So I don't have much to contribute about them.
I know nothing at all about UCI, except that their students seem happier than those at some of the other UC's!
I hope this helps! Waiting is terrible!