I can't say much about how BBM has changed or affected society because I'm living abroad and have been a long time, but it did impact my life personally. It made me aware of my own loneliness and isolation, more aware than ever before, and of a need to really do something to change that instead of letting it go as a hopeless situation; impossible to change.
I first started writing and communicating with people here, then I set out a plan to at least place myself in situations and locations where I might actually meet someone to date. I'd been living quite alone for years, you see, and I mean alone in the sense of not "seeing" anyone. I had/have friends, but wasn't dating.
This had partly to do with the breakup of the long term relationship (15 years) with my former friend and lover. That was very hard to handle and I just didn't feel like trying anymore to meet or date anyone. But the power of BBM got through to me and I started over!
Since then, which was only last Feburary (2006), I have gone out, met people, made more friends and even met someone I have a lot in common with and well, we hit it off, and are dating! Yeah, it's funny that it took a movie to "get me going" again, but that really is how art works on some people and why art is such an valuable and precious experience.
So, that's a little on how Brokeback Mt. changed me. It "got me good" and because it did, I got myself going and made my life better. I hope others do too. I don't come 'round as much as I did when I first started out here, but I'll be in touch.
Happily,
Rayn