I stumbled upon Rob Cockerham's Starbucks Chair Prank at 5th and Howard, which is still going after a month and a half (probably a new record for Rob's public pranks). Someone spraypainted over the Starbucks logos but no one has cut the locks. I walked by them three times during my stay in SF and I did see one person sitting in them, but didn't get a chance to take a photo of it.
Maybe this will be like the 5 Freeway prank artist Richard Ankrom did. No one seems to mind it and some actually find it useful.