Resurrecting a dead thread, because I've just gotten bitten by Yelp's policy of blocking all TOR exits (I assume because they're using something like Emerging Threats' TOR list). What Yelp should do is run their own TOR exit node and throttle connections from the TOR network as they see fit. If the TOR network sees an exit with the same address as the one being requested, it'll route all traffic through that exit instead of using other exits. This way, Yelp can have direct control over how much TOR traffic it will accept. This solution doesn't address the problem I have, however, which is the fact that I run an exit node, but I don't use the TOR network. My IP is still blocked, even though I'm not trying to access Yelp via TOR.
I think, overall, the problem is that Yelp is, as +Griffin Boyce
says, using a hammer where a feather might better serve. Simply blocking a network because of a few bad apples is a policy which, if universally applied, would leave Yelp in a very small box.
Finally, Amber, I know you don't work for Yelp anymore, but perhaps you could give us a way to contact someone there? The emails I've sent to support addresses aren't being replied-to.