I'm frequently in San Diego and LA for work.
On the freeway its WONDERFUL. I'm a bit more cautious than the normal biker I see. 40mph is about where I am comfortable doing it, bit slower mostly. I will split single pair of road blocking cars at freeway speeds if they are just staying next to each other at or near the speed limit. But it has to be worth it for me, as in no cars in front of them going to make me just have to do it again.
Surface streets, generally only in a long line will I bother to split, or coming up on the freeway entrance so Ill want to be first.