I have started going to an independly owned coffee shop called Rendez Vous Café at 106 S. El Camino in San Mateo.
It is a good alternative to Starbucks-plus there is legitimately free wireless access-you do not need to pay T-mobile, or anyone else.
Coffee good and staff are friendly.
Hours are very early - I hear 6:00 ish to about 6:00 pm M-F. Weekends they close earlier I believe.