At least you won't have to deal with any unplanned pregnancies.
Not to make light of it - I guess if my daughter had all female friends who were lesbian, I might have to wonder if she weren't lesbian herself. Not that I'd get upset or anything, but yeah, I think you'd proceed a little differently if you knew your child might be dealing with the issues that being a gay teen brings as opposed to those being a heterosexual teen brings.
It's not productive to pretend that you're child being gay and your child not being gay call for the same sort of interactions and responses as a parent.
My roommate my senior year in college was a lesbian and that about drove my mom to distraction. I didn't tell her- I didn't have the chance to - C & C (my roommate and her girlfriend) gave me a ride home from college one Christmas and spent the night at my house and my mother didn't even have one of those little devices Joe just posted - but she knew- she said, 'Those girls are more than just friends.'
I didn't lie to her- I said, 'Yes, they're lesbians' and my mother was like, 'Rebecca Jean - you have to get a new roommate!' I don't think she ever thought I was gay, but I know she thought that everyone else would think I was gay. I told her not to worry about it and was roommates with C. and (essentially C- she slept over almost every night) until I graduated.
Years later, several people did tell me they thought I was gay because I lived with these gay women and seemed to like them- but it never stopped anyone from being my friend (that I know of).