Yesterday I posted a slightly irate diary about the presence of ads on Daily Kos, even though I'm a subscriber. After some research and help from wonderful folks in the community, I tracked it down to a browser problem, specifically Chrome for Windows (I run a dual boot Mac OS/Win7 system so I can play some Windows-only games).
Could not determine any specific adware that was triggering them. And then this morning, I saw some scrolling ads show up on a game forum I hang out on. I'd had enough.
A quick uninstall/reinstall and looks like the issue is solved; I think I may have gotten some bad code somewhere in Chrome. I'll keep a close eye on it though and make sure it doesn't come back.
Thanks to the community for your help and support.