Watch out, Burning Man buffs (and buff nakeds), that man with the LED poi sticks and American Flag thong might not be really really REALLY happy to see you, it could just be a Fed with a gun nuzzling his junk. (Or American actor, Matthew David McConaughey.)
Most of the undercovers are there to bust people for drug use, so it's probably best to be careful on that front at the playa. Last year, the Reno Gazette reported on 350 arrests during the fest — but that's a tiny drop in the drug bucket when you think about the 50-60 thousand expected attendees.
Or just don't go and enjoy your fantastically peaceful city — especially if you live in San Francisco. Man, Burning Man weekend is the most wonderful time of the year in S.F., the air's a little cleaner, everyone's a little nicer. You can go to brunch at a reasonable hour. It's marvelous.