They've started popping up at Bay Area markets as early as Memorial Day weekend.
We held off on buying any until a couple of weeks ago, particularly after I spied some Early Girl tomatoes at one of my favorite vendors at the Ferry Building market.
They weren't as good as they were last year. Word on the street is that peak season starts around August, which is pretty similar back to when I was living in NYC. Oh well. maybe I can force myself to wait a few more weeks....