In Houston, you would be able to manage without a car if you lived and worked in the Medical Center. There are several apartment complexes right off the light rail so you could take that directly into the Med Center for work.

Of course, doing anything else would be difficult. You wouldn't even be able to go get groceries, though I think there are a couple of complexes that do have shuttles to the Fiesta by Reliant.

Also, in Houston, you will not be able to enjoy the gay nightlife (which is a lot of fun by the way) if you don't have a car. There are no cabs. Well you could call a cab all the time if you really wanted to, but that would be a pain.