I personally use it on around 50% of my sites, where I dont want to be contacted, I wouldnt consider selling.
this got me thinking, would anyone actually considering paying, say $5-$10 depending on portifolio size for a year, that year entitles you to change the whois on unlimited domains to a privacy protect service, with email forwarding or blackhole, and a guarantee of never disclosing whois information unless forced, I could operate something like this offshore