So the first week of September (Labor Day Week), I went out to San Francisco for a night, did Napa Valley for a day, then Yosemite for 4 days. We stayed about 30 miles outside of Yosemite, which equated to about a 30 minute drive to the entrance along 120. (I'm told the entranceway from the south, Fresno area, is the best way to do it). It was cheaper than staying in the Valley, and worked out fine. We put a ton of miles on the car, but it was a rental. Driving Yosemite is tough because it's almost all one-lane roads, and you have to hope people are paying attention enough to pull out. I can imagine it being MUCH worse in peak times (any time from May to the days before we got there). Also, unless you like big trees a LOT, I wouldn't really recommend the hour-hour and a half drive to Mariposa Grove from the valley. Glacier Point, definitely.

That's all, enjoy.