I've never seen any reviews or specific comments on the showers at the SFO International terminal, so I decided to check them out last week on a long layover.
For those who don't know, the showers are located within the
SFO Hairport salon located in the International Terminal. If you're on the "G Gates" side of the terminal, head toward the escalators (opposite the entrance to the BART terminal). Left of the escalators is an overhang hallway that leads to the salon. As far as I'm aware, these are the only public shower facilities within SFO. Unfortunately, the salon (and showers) close up somewhat early. Hours of operation are 8:00 a.m. to 5:00 p.m. Monday-Saturday.
I arrived in the early afternoon and asked the woman at the desk about taking a shower. She said the rate was $11.00 USD. This is a rather high price, and I asked if I could see them first, to which she responded,
"No. It's just a shower." 
I asked if the $11 was for a specific time limit, and she said no, however "If you're in there for 2 or 3 hours I'm going to come and get you."
So don't expect great customer service for your $11, but as I was on a FT mission to explore the showers, I opted to pony up the cost and check it out.
I think there are 3 separate shower rooms. Each is about 6 feet by 9 feet (perhaps 2/3 the size of the nice shower rooms at the UA RCC in NRT). However they aren't nearly as nice looking as most airport lounge shower rooms. Each one is a single-level tiled room, with a drain, partially divided, with a sink, and then a small shelf/seat. There is a curtain separating the shower from the rest of the room, so there's no chance your luggage will get wet.
I did notice there was no lock on the door of the room. I assume the shower matron notes which shower(s) are in use, and if the door is closed, that generally means it's not available. I mention this in case it's an issue for someone, however, and I did keep an eye on my stuff throughout my shower.
As I mentioned, the facility itself isn't pretty. Think
typical dorm room shower. It was clean, however. The only amenities provided are a towel (smelled and looked clean) and a small bar of soap. The
Hairport sells pretty much every other basic shower/hygeine supply you could need, however - though you'll pay typical airport price. I did wish that a bathmat or second towel would be provided, and perhaps I will make this request if I return.
Overall, the shower was a good experience, and I wouldn't hesitate to use them again when traveling through SFO. The price is a little steep - then again, what isn't in the international terminal (except for BART)? But if you're looking for a decent place to get clean, then it is certainly that -
decent.