Google announced a minor revsion to its AdWords policy regarding multiple display URL domains per ad group.
Google will no longer allow for multiple URL domains within a single ad group. Moving forward, display URLs within an individual ad group must have the same top-level domain, regardless of previous exceptions or acceptability of any ad groups.
The display URL (limited to 35 characters) is the URL displayed in paid listings to identify your site to users. The purpose is to give users a clear idea of what website they will be visiting when they click on an ad.
Google now recommends using separate ad groups for each domain, as it will provide a better user experience for your potential customers, but will also allow you to better organize and track the various domains within your AdWords account.
[Upgrade to a professional-level membership from Website Magazine]