Just in case you didn't hear about this yet--Google Adwords has changed their policy regarding subdomain displays:
http://adwords.blogspot.com/2010/01/...play-urls.html
Beginning this week, all ads leading to sites on hosted domains will need to have display URLs that accurately reflect their destinations.
Let's say I wanted to create an ad linking to this blog: http://adwords.blogspot.com. In the past, blogspot.com would have been an acceptable display URL. Because there are so many independent blogs hosted on http://blogspot.com however, we now require the display URL to reflect the specific blog reached upon clicking the ad? in this case: adwords.blogspot.com.
Incorrect:
Destination URL: http://adwords.blogspot.com
Display URL: blogspot.com
Correct:
Destination URL: http://adwords.blogspot.com
Display URL: adwords.blogspot.com