incrediBILL - 5:33 am on Sep 2, 2010 (gmt 0)
I'm not sure if it's the same parking company, but one of them got outed for cloaking special "ads" to Google. If you were a visitor, you saw normal PPC ads on their domains. However, if you were Googlebot, they showed you a special batch of "ads" with direct links to domains they were promoting.
Probably would've gotten away with it too except one morning I wake up and they're in my #1 spot with over 5K backlinks all from domain parked pages to the site now above mine.
After seeing a domain park play that way I'd never use one to park a domain I wanted to ever use in the future, that's for sure.