Ads have become a REAL problem, and are no longer an innocent way of funding bandwidth etc. Sourceforge has been like this quite a while, and as suggested, other 'legitimate' companies are now bundling crapware along with the stuff you want (Adobe - looking at you).
There's a forum I use regularly (harmonycentral.com) that runs syndicated ads, and recently there was one that a) spawned a new page within seconds of arriving b) started playing audio automatically and c) spawned a new page every 30sec with the audio out of sync with the first. Within a few minutes the site became unusable without ad blockers working.
I always took the view that ads funded the 'free' sites many of us enjoyed, but this was madness. I mentioned it to the forum admins, but they were not aware of the ads being run (syndicated out, choices made elsewhere). There have been problems on other sites with flash-based ads too, although none as severe as this. So now I just run with ad blockers on all the time. It's not good, because I'm sure it's denying a revenue stream, but it's either that or stop browsing many otherwise useful parts of the net.
I can see the golden goose laying in the corner, throat cut.