Re: San Fran/ At&T Stadium
I just got back from San Francisco in May and did just about all the things mentioned above, and they're all good suggestions. I can confirm the sea lions are still at Pier 39.
We went to a Giants/Nats game, and it was great; you'll definitely enjoy it. We grabbed a few beers at 21st Amendment before the game, and I would recommend it if you like microbrews. Make sure you buy garlic fries at AT&T.
We were also there for about three days, and in addition to the things mentioned above, we enjoyed Golden Gate Park (it's huge), Land's End and Ghiradelli Square.
Definitely make sure you pack for all kinds of weather because it can change drastically and in a hurry. I've only been twice, so I'm certainly not an expert on the city, but if you have any others questions, feel free to ask, and I'll answer if I can.