I've always thought lesbians were far more 'socially acceptable' than gay men, for the reasons that people have mentioned (but mainly I think because most of straight society are completely disgusted by anal sex basically, whereas gay female sex doesn't offend as many people) - this is my interpretation anyway, although that might just be because of the people I have come into contact with, and specifically my friends and family's feelings on the subject. However, maybe one way to work out which is the more socially acceptable is to view society's reactions to certain things e.g.
1999: Queer as Folk is shown on British terrestrial TV with fairly explicit gay sex - from what I can remember, this caused quite an uproar in the media, and their were reports of complaints etc
2002: Tipping the Velvet shown on British terrestrial TV with lesbian sex scenes this time - again, from what I remember, there was a lot of media attention surrounding this show, but more of a nudge-nudge wink-wink attitude - with the media mostly describing it as a "titillating romp" than as something offensive. This is hardly a desireable situation - lesbians wouldn't want TV to eploit them just to excite straight men, but again there was less of an angry reaction.
Then again they were spaced three years apart, so who knows how much that will have affected reactions. It is sad that in 2004, a number of Brit tabloid headlines read "Sick Sex Shown on TV" for a single, brief gay-male kiss on a pre-watershed soap. I mean, for God's sake!! Society is hardly going to crumble! But then I hate pretty much every tabloid headline... if I had my way, they would all be gone!!