A new, and logical, Google AdWords display URL policy was announced this week. In summary, if you are on a public, hosted domain, you must show the subdomain that you are using in your display URL. For example:
Incorrect:
Destination URL: http://adwords.blogspot.com Display URL: blogspot.com
Correct:
Destination URL: http://adwords.blogspot.com Display URL: adwords.blogspot.com
Incorrect:
Destination URL: http://subdomain.wordpress.com Display URL: wordpress.com
Correct:
Destination URL: http://subdomain.wordpress.com Display URL: subdomain.wordpress.com
There is discussion, not much discussion, but some, at WebmasterWorld and DigitalPoint Forums. As expected, the WebmasterWorld feedback, so far, is positive to this change, saying "this is how it should be." As expected, the DigitalPoint Forums feedback, so far, is negative to this change, saying "thats bad for adwords users."
Personally, it makes sense to have this policy and I agree with it in most cases.
Forum discussion at WebmasterWorld and DigitalPoint Forums.