http://www.wisconsinoutdoorfun.com/article/20110620/WOF02/306200051&located=rss
Here's info on Madison, Wisconsin's June 19, 2011 naked bike ride. The city has no ordinance banning public nudity, but riders can be cited if an onlooker complains.
At some point last week (too tired to find the link), some participants filed a lawsuit seeking an injunction stating that they could not be ticketed for nude bike riding. The judge (Judge Sumi, same circuit court judge involved in the open-meetings law violation re: the collective bargaining vote, if you're following WI politics) declined to issue the injunction. I think the cops handled it somewhat better this year (at least one of the citations issued last year was defeated in court, and I think a few more might still be making their way through the system, which seems like a waste of resources to me). This year, they just asked for a volunteer to be cited.
There's also some history here. My memory is a bit fuzzy but if I recall my Madison history correctly, some years ago (the 80s, maybe? It was before I lived here, anyhow) a few women were cited for being topless at a beach where some guys were also topless, and there were claims of sex discrimination. I can't remember how it turned out (I
think the citations were dismissed), but that was one of the issues re: last year's bike ride--that guys who wore shorts but were topless (and it's Wisconsin--trust me, there are plenty of dudes here who really, really should keep their shirts on but don't) were deemed fine, but topless women wearing shorts were cited.
Anyhow, my favorite bit from the ride--the guy who painted on his back, "No Dangerous Emissions" with an arrow pointing, um, down (think he was at last year's ride, too). Not something I'd participate in (and there are a few images I wish I could maybe unsee!), but I love how weird my town sometimes is.