Guys,
I was in Mexico a couple of months ago and prior to my travel I went to the Mexican Consulate in San Francisco to make sure that I don't need a visa. The officer who was in charge of visas didn't really know whether I needed visa or not (at that time I had RTD only, no GC). Then he decided to stamp my RTD with a special stamp "Exteno de Visa", meaning no visa required. He also gave me the immigration form that is usually given to all the passengers to fill out before they arrive to Mexico (Mexican verision of I-94) with the same stamp. Very nice experience. Althought I received my GC one day before my departure (Yeahh!!), I had no problems entering/leaving Mexico. If you live in the Bay Area, visit the Mexican Consulate if you want to obtain that kind of stamp.