Yeah, another confirmation that the 1st onramp past the Golden Gate bridge works. Though you'll probably wait a little bit. I've hitched here twice and it's taken me about an hour each time. Not too bad.
You can also take a bus to Santa Rosa for pretty cheap, about $5 I think. I've heard this works even better. Look online for schedules and times.
To get to the GG Bridge, take a bus. It's a good walk otherwise. About 3-5 miles from Golden Gate Park.