As I am a small shop catering specifically to internet industry professionals, I have not seen this to be a big deal.
But I imagine for a shop that caters to end-users, this could generate some nice cash.
But as I am working with people who know that they can get PPC traffic from their Domains, and much better PPC than WWD is paying, I really don't expect to see any cash from WWD for PPC since they have a $50/month payout threshold.
I mean, I have some 600 Domains and they only make me a little over $60.00 a month now (though this monthly revenue stream is increasing with each passing month). But these Domains are parked in places that KNOW and understand PPC parking like
Fabulous,
GoldKey,
NameDrive and
DomainHop.
So I think if you are interested in parking cash or PPC revenue streams, you would actually park your own domains on a proven system. Any income generated by a customer not using there own domain has to just be considered gravy and really can't be counted on.
But, that's my 2 cents. -Doug