I just installed the premium Domain Mapping plugin and followed the installation directions. It seems to almost work perfectly. The default url would have been http://www.hatchesmagazine.com/blogs/1080fly3/
The custom domain for this blog is http://1080fly.com which when viewed in the browser the main page loads just fine.
The problem is when you click on any of the post, category or any other links. It just returns a 500 server error. This page is an example: http://1080fly.com/2009/09/20/hello-world/
I have searched the forums and have not had much luck in figuring this out.