Most say, no, it does not earn them any or enough money to keep them live on their site.
In the twenty plus replies about how much people are earning from Referrals ads, there was not one single positive reply.
Many have dropped those ads completely from displaying on their site:
It just didn't work for me. After trying referrals for a couple of months with virtually no conversions, I took it off of my site.
Forum discussion at WebmasterWorld.