One of my former co-workers described wild doings in the pre-AIDS era, so I imagine promiscuity would be more common.
Well, I suppose it depends where you were. There were some pretty wild scenes in selected places (there still are, Berlin is quite an eyeopener). But they were notorious and only in a few places, certainly gay life in my city as a Pre-AIDS era teenager was fairly quiet, there were only a couple of bars, no public sex venues and whilst there were supposed to be some "parties", it was only amongst a selected group. One night stands were no less or no more common than now. These days, there's a dozen bars, three PSV's and I don't know about the party scene, but I suspect it's out there. I suspect this confidence and openness may well have come 5 years earlier without HIV.
From about 85 onwards, there was a genuine fear of HIV and in general people did nest and go monogamous and were more careful. That started to die off around 2000, as therapies made people think they could lead a perfectly normal life. There's a lot of foolishness these days, particularly amongst younger men and because there aren't many visibly ill people, because there isn't the constant funerals, the fear has gone. It's very easily to hook up off the internet as well. I'm no oil painting and in my mid-40's (which is like 90 in gay years), but I logged onto a site just after Christmas to give some friends seasonal greetings and to catch up with gossip. In the hour I was on, I received six proposals from people in the City I was in.
I do live a relatively normal life, I am pretty well 95% of the time, but the side-effects of the medication can be pretty brutal sometimes and I do get tired easily.
I still think the biggest overall effect will be Southern Africa - where remember the main mode of transmission is heterosexual. There's going to be a lot more economically active people, what the overall effect of that will be, I don't know.