I'm sorry this is going to be a long review, but that's just because I had such a great experience with the CityPASS!
My boyfriend and I were in town for 3 days, with no rental car and no concrete plans. This pass was perfect! We picked up our passes at the Visitor's Center inside Macy's, since it was right across the street from our hotel. The first day we took the Muni out to the Museum of Science. We spent about 3 hours there, we did not pay to do the planetarium, the general admission was perfect.
The second day, we jumped (literally) onto a cable car and took it all the way up to Fisherman's Wharf. We took advantage of our aquarium admission, and spent maybe an hour inside. It's small, but cute. We then jumped in line for our 1 hour boat tour. We only waited about 20 minutes and were able to enjoy our tour.
Throughout our visit, we hopped on and off the Muni, whenever we didn't feel like walking.
This is a must have pass, just for the unlimited rides alone!