You have to recur.
Seriously tho you have to have decent referrers to track incoming traffic. Nats for example.
It is amazing how many progs still have less than optimum referrers.
I've noticed that most winning progs now days have good solid referrers. I like to see Nats. If i'm going too buy traffic and send it, (as I do, all forms) I like to see a sponsor have Nats.