Every time we're in Ft. Worth, we go straight to Cabo Grande (Sundance Square) and order up a couple of their frozen strawberry margaritas - the big ones of course (schooner). These guys deliver a consistent, flavorful drink that is one of the better frozen drinks we've ever sampled.
Cabo Grande has a nice little bar area in the back corner which has floor-to-ceiling doors that open onto the sidewalk. They don't always have them open, but when they do, it really adds another dimension to the place.
Get there early to take advantage of happy hour and be sure to get a bowl of queso dip to go with your margarita. If their is a special event going on downtown, it will be crowded, so again, early is better.
Once you wrap up with happy hour, move over to the dining room for plenty of great food choices and a chance to sample some of their other margarita flavors.
Though their frozen strawberry margarita is a machine-made drink, we have always scored it pretty high and are leaning towards a 4 of the limer scale.