We've gone to a handful of Stanford games the past four years... we've won a few tickets for free on the radio, a neighbor gives us free tickets every once in a while, and sometimes we've bought them for 50 cents on Friday night... but unless they are playing Cal, Oregon, Notre Dame, or USC, there are usually less than 25k fans there.
We went to their season opener two weeks ago... granted, it was against UC Davis, but this was a team coming off a bunch of consecutive BCS bowls, and there were MAYBE 20k fans in the house.