I block tor from many of my servers. I started noticing that whenever I had an issue with someone attacking a server the source traced back to an exit node. What I found when I looked at the traffic coming from the exit nodes was that the vast majority of it was malicious. There was a massive amount of automated password guessing, exploit attempts, and attempt to connect to botnet controllers/backdoors.

I'm all for anonymity. However, until the tor project puts some effort into outbound traffic filtering for exit nodes it is too much of a time sink and headache not to just blackhole it all on servers that either do not serve public content or where anonymity really isn't needed/justifiable.

I put the code I use to block tor exit nodes in the public domain. You can download it here: https://github.com/vab/torblock