Excellent, but not for everyone.
I live and work close to Yamo Thai and have been eating there for 5 years. The food is inexpensive and delicious - best bet is the curry of the day washed down with a Thai iced tea.
Yamo isn't for everyone. The decor and the chef/owner are both unique. Its small and not terribly well-ventilated. The chef and her son both have a unique sense of humor that exceeds even what most San Franciscans consider to be sarcasm.
But if you know good food, and can get past any pampered, Western perceptions you might have about restaurant decor, this is a restaurant on par with House of Nanking, Tu Lan and Country Station Sushi. Excellent, but not for everyone.