On Heroku, someone reported my site as being infected with malware that stole peoples Facebook passwords. Heroku took the site offline and notified me. I explained that it was just a web proxy and that there was no malware or stolen passwords. A week or two later they emailed me that I was correct, but they were going to keep my site offline and change their TOS to forbid proxy sites. (As far as I know they never did change their TOS, so GoPee should still be safe.)
On Nodejitsu, someone tweeted links to porn that went through my proxy, and they disabled the site thinking that I was using their service to host porn. The CEO told me that they'd turn it back on if I added user accounts and a way to ban users. But at that point, I had a newborn son and was in no mood to put a bunch of development work into making my anonymous proxy not-so-anonymous.