I am adding MVC to a project that has MANY legacy webform pages. This works fine. However, I currently have a separate masterpage for MVC and for the webforms. The two master pages produce essentially identical output. I'd really like to kill the webforms one and just use the MVC master page with all my pages and stay DRY.

Not being DRY has already bitten me a couple times when I forgot to change both.

I tried doing the obvious way and just pointing the webform content page's MasterPage attribute at the MVC masterpage. This throws an error saying the MVC masters only work with MVC views.

This seems like it would be a pretty common problem with mixed MVC and webform projects. My MVC master isn't doing anything with ViewData, so I don't see any reason the webforms couldn't use them.