I will give a brief overview of the glbt environment at some of the schools I have interviewed at:
Texas A&M: It's in College Station, TX. Gays should avoid this school like the plague. (unless of course you're the type that wouldn't mind being shoved back in the closet for four more years)
UT Southwestern: Not really addressed in the interview orientation, though I did run into one lesbian who's a first year there who seemed to feel that the environment at UT Southwestern was 'on par' with most other schools. There is a gay group on campus that has about 5-10 regulars that go to meetings -- their events don't face many difficulties in getting organized... Sadly, the Office of Diversity and Multicultural Affairs doesn't incorporate them into their office's mission.
Baylor: Probably the most gay friendly school I've visited in the South (probably about the same as Rice University, where I go for undergrad across the street). There is an active gay organization on campus (much to the dismay of the UT-Houston administration which prides itself on NOT having an LGBT organization on campus) and most students are very accepting and many consider themselves allies.
Emory: Decently gay friendly. Though, when asked a student about the lgbt climate, they needed to have the term explained to them, after which they gave an odd face and responded that they didn't know of anyone that goes there 'who's like that'. Atlanta is a saving grace, though.
Yale: I declined my interview there due to the cost of flying to Connecticut (late in the interview season, so I was kind of tired of the whole process), but I was very disappointed in the fact that the hosting program offered no LGBT hosts, nor could any be found after I specifically requested one from the hosting coordinator. Shame on you, Yale.
Harvard: It's in Boston... I think that's about all that needs to be said. One interviewer did seem a bit taken aback by my heavy involvement in LGBT civil rights organizations, but of course she was from kansas, so I guess that's to be expected. The other interviewer got very excited by my campaigning for Dean and went on a tirade about the importance of gay rights legislation/court decisions, etc. She and I got along greaaaat. Overall, students seem rather prep schoolish, but I could tell that the thought of a gay peer wouldn't phase them a bit.
Johns Hopkins: Didn't get much a feel for the gay scene at all in Baltimore, but judging from what I did see, I wasn't very impressed. The Admissions Dean was black and possibly gay, so that was a plus, but other that that it seemed like the administration had kept the gays a good distance away from the interviewees.
Columbia: New York, of course, is a very gay friendly city, however it seemed as if Columbia hasn't quite caught up... The school seemed very traditional and not so interested in attracting lgbt students. I did stay with a gay host while I was there, though, and he was great -- gay students are definitely out there, but it seemed as if they take a much lower profile than at some other northeast schools.
WashU: The school is right next to the gay/yuppy/metro side of St. Louis, so the school seemed to be in an isolated hotbed of gay activity in the midwest. I watched a student-run screening of Philadelphia while I was there (World AIDS Day) and there was a pretty good sized turn out (many gay students as well as allies). Though, be forewarned, once you leave the safe confines of the campus, attitudes towards gays and lesbians change drastically amongst the general populace.
U. Penn: BY FAR, the most gay friendly school I interviewed at... There are about 20-25 openly gay/lesbian students at teh school right now (which is a fairly large number considering the fact that there are about 400 that go there at any given time). The school has a ridiculously large three story gay and lesbian center (that it shares with the undergraduate campus) and they are constantly trying to draw in gay/lesbian students (they even talked about lgbt students/campus life during the large general orientation, much to the dismay of some of the brigham young kids that were interviewing at the time, haha). I stayed there with some of the coolest gay kids who are first years there right now who took me around Philly and showed me what Philly gay night life has to offer -- I was very impressed, the gay scene reminded me of New York, except on a smaller, more manageable scale. Couldn't have asked for more in terms of lgbt campus life!
In general, though, I would suggest that you be open about yourself and your activities on your application and when you are in your interview. Would you really want to go to a school that discriminated against lgbt students? If you don't really care, then by all means closet yourself during the application process, then come out as a flaming homosexual when you get out so you can rub it in the faces of all the bigoted admissions officials