I'd prefer greater frequency and longer trains, but my two SFO trips on BART have been very pleasant. It takes a little longer, but with online check in and more predictable TSA lines, I can leave my home in Berkeley 2.5 hours before a domestic flight and be confident that I'll arrive at SFO with time to spare. It's low stress and I can catch up on my reading.

They just don't seem to have the riders to justify the Richmond to Milbrae route. I wish they did, but no biggie.