Definitely do it. There are quite a few here on GA who are doing it... there's a thread somewhere about it. I did it last year. Death by Dreaming is the story I wrote. It's a fabulous feeling. You set up your page and you keep a running total of the words you've written and it's exciting to see the purple bar go up and up. You may not finish it, that's okay, although you get a cool certificate if you do
As for the story you write, you don't have to be gay to write a gay story. You don't have to admit anything other than that you are interested in exploring that area. Take a look at some Yaoi pictures for inspiration and you can then say that you came upon Yaoi and thought it would be intersting to write a story based on that kind of thing. If you're creative there are all sorts of reasons to come up with if necessay without having to admit you're gay.
Anyway I digress and am probably talking a load of shit but I love NaNoWriMo and I would heartily recommend anyone to do it especially if you have a group to do it with. Think about how excited you all will be and you will make new friends and have a whole new sense of achievement.
The main thing is not to get too hung up on the story. As you said its the quantity and not quality, so just sit down and write whatever comes into your head. It's surprising how quickly a few thousand words can flow out of your fingers
There are 30 days in November so that's a target of 1666 words a day. It's not like writing an essay because it's fun