I know very little about library science but I do have a couple friends who are currently seeking a Masters degree in it. So I will share my limited views (definitely not 100% on these answers, mind you):
What do they do?
1. From my experience they spend a lot of time helping research. They research in different ways. Help other students/professors/the public in general etc. find helpful information & provide guidance to the type of steps they may want to take with their research (I think this can be a very daunting task).
2. Research themselves about, well, library science. They study the demands of the library/what areas are weak/ organizational methodology/ study theories of libraries (etc., etc., etc.).
3. Oversight of the other non-professional librarians (training, helping them understand the system, monitoring them etc.).
4. Replenish areas needing development/ methodologically diminish areas that might need to go (IME this is a very political process).
5. Write research studies/articles/commentary about library science (I think this is more academia and less public libraries).
6. A LOT more going on behind the scenes that I'm not aware of.
Is it difficult?
I think it's a fairly difficult job that, on the surface, is made to look easier for and from the public perspective. Additionally, I hear getting the actual Masters is very difficult. The programs are competitive, there's a lot more science than it seems, the work is long and tough. I don't want to overplay the difficulty though, it's not going to be astro physics.
Libraries closing
I think there will always be a need for academic libraries. I use the online search engines/my librarians both a LOT. I always go to the library to study because it's so much more useful than at home. I see the same thing with other students. Plus, people will always need direction on what they want to read/need to read etc. Yes, I think public libraries might start feeling the online shift but I think academia feels this less. I could be wrong & this would be a concern of mine as well. I'm guessing if you have access to academic search engines tons of articles about this have been written by librarians.
Only heterosexual male working at one
I guess maybe it depends on what kind of library you want to work at. I know, personally, that corporate and academic libraries have lots of males working there. However, I can't lie. My fiancee's mom is a librarian at a public branch and they're all women except maybe one guy. I wouldn't worry about it (more girls to schmooze? right? j/k

).
Good luck dude! If I weren't doing what I'm doing now I would have considered library science TBH. I think it's a great field. Have you considered talking to some local librarians and/or the program at U of T about your concerns?
