Restaurant employees in San Francisco are advocating for a standard 25% tip. The current norm for tips is between 15-20%. The IRS says that 15% is about what they estimate for workers, and some are dubious that employees would report extra tips over that percentage. Others feel that restaurant employees should receive a wage, rather than be dependent on tips for their income. The workers have the backing of some restaurants in the area.
See "San Francisco restaurant workers support 25 percent tip standard", Ed Arnow, The Mercury News, October 13, 2011