I see quite a bit of people ride Greyhound to/from the San Francisco Transbay Terminal, the routes going to LA and Reno/Sacramento are the main feeders into SF. I took their BoltBus between Seattle and Vancouver last year, it was my cheapest option but it was nice driving up the 5 out of King County and through rural Washington up to the US/Canada border.
First has done a good job of rehabbing the Greyhound fleet, their new MCI D4500s and Prevost X3-45s look classy with the new livery. They just need to do the same to the terminals - I go past the Oakland terminal and it's not exactly nice.