Puerto Alegre—don't be fooled.
I'm old and stuff, so I remember Puerto Alegre circa 1997: divier, dirtier, drunker and delicious.
A lot of misguided overly nostalgic San Franciscans will tell you that Puerto Alegre is still the queso grande among the numerous Mexican eateries in the city. They are wrong. Do not be taken in by them. It used to be good, but now it's not.
Like so many things (myself included) age has not improved Puerto Alegre. The seedy and wonderful taqueria with the hyper-crazy-killer margaritas has been replaced with a ghetto-tastic version of Chevy's. But at Chevy's the chips are better.
We were there most recently with a large-ish group for a birthday party. Our single waitress deftly handled us and kept the margaritas rolling in. She was great. The guac was nice and chunky and good. The salsa was bland, as if they've had too many gringos bitching about the spiciness so now they're serving glorified ketchup instead of salsa. The BF and I shared a whopper super burrito, a chicken tamale and a cheese enchilada. The tamale and the enchilada were barely warm, the burrito consisted of 90% dry, tasteless rice, with a splash of meat and a soupy dollop of sour cream. The beans that came on the side of the combination plate were watery and bland, and, hooray! yet more dry, tasteless rice!
The margaritas, once limey, tequila-y goodness were overly sweet and chalky with sweet and sour mix that contributed, I'm sure, to the crazy indigestion that ensued later in the evening (that was also not helped by the meal itself.)
Every time I go to Puerto Alegre, I stay up half the night, my stomach burning and gurgling, wondering if I'm going to have to make a dash for the bathroom, and every time I vow never to return. But somehow I do.
And somehow, it's always a good time... It's truly a mystery to me... I guess the trick is to make sure you choose your company for the outting wisely.

