I'm going to be in San Francisco for a week at a conference and would like to rent a bike for two or three days. I'll be staying near the airport so getting into town requires mass transit (I think it's called BART). Once rented, is the bike allowed on BART to get back to the hotel? Thanks for any input.
The most popular bike rental place in SF is Blazing Saddles. I think they have 4 or 5 locations but all of them are in the Fisherman's Wharf/Pier 39 area where most tourists eventually end up. I see the Blazing Saddles bikes on the Golden Gate Bridge all the time. They are all hybrids and come with a handlebar bag. You can get route maps from their store.
If you're staying near SFO, you're better off taking BART or the train into the city (the train is really comfortable and a great ride) and then head towards Fisherman's Wharf to rent a bike just for the day. I wouldn't carry it all the way back to your hotel near the airport (which is pretty far). Once you're in Fisherman's Wharf, it's real easy to cross the Golden Gate Bridge and head down to Sausalito and Tiburon -- that's a scenic and fun ride.
There might be some local bike shops around South Bay that do rentals, but I don't have any info on that so perhaps some other Bay Area folks can chime in with what they know.
If you like a tiny bit of hill climbing, I would definitely do the short climb to the Marin Headlands and then down to Rodeo Beach before heading down towards Sausalito. You'll see some great scenery!
I'd also recommend doing a loop around the city -- from the Embarcadero up through the Presidio and down to Ocean Beach/Golden Gate Park, and then ride back downtown by cutting through the Haight. You'll pass through a lot of interesting neighborhoods.