I don't shower with people I'm not in a sexual relationship with otherwise. So, not so much for gay people (I'm straight), but I've showered with a bi guy.
To take the question two steps further, if I had to pick between showering with gay or straight woman or gay or straight man I wasn't in a relationship with, decision tree would be:
-level of trust/what I know about the people I'm choosing between (is it a friend I can trust to be respectful? Is it a friend I can trust NOT to be respectful and I'll never be able to look them in the eye again?)
-the lack of possession of a penis (would rather shower with same gender)
-and then... honestly not really sure. I think that competitive and bitchy would be a bigger problem for me than sexual orientation. So would degree of staring at me. And, obviously, handsiness. And none of those would have to be related to sexual orientation. *shrug*