I have dined out several times since I came to the Bay Area in May, and I have found that the tip has been standardized on the checks: 15%, 18%, and 20%. Pick one, and the bill also shows how much you have to pay in total.
In Taipei, the 10% service charge is a compulsory amount added to bills for most restaurants. Considering the different living standards between the two places, I think the tips in the Bay Area are acceptable.
Well, begging for tips in a nearly coercive way is another story. Please see the following report.
乞討式小費，專坑出境游中產_風聞
