This topic has been covered here several times (there was a thread about parked domains just a few days ago). The consensus seems to be that AdSense for Domains won't generate much revenue unless you have a lot of traffic on parked domains.

Thanks signor_john, I must have missed those.

I've once tried to try it out on a domain and for unexplained reasons they even refused to play along citing "policy violation" as reason without saying what part of the policy that would be (I could not find any reason, not even remotely why they'd say that. Of course they didn't reply to the question for a bit more clarification.

Combining such a policy with reports of it not earning, and my dislike for parking services anyway makes it somehtign I'll never try again.