Sorry I got to this late, I've been stuck with a very slow internet access.
The new version of the domain mapping plugin is now up and available as no doubt you have spotted.
The changes in this version are:
1. Domain redirects. In the front end of the mapped blog, any request for the old domain will now 301 redirect to the new mapped domain. This works for both sub-domain AND sub-directory installs: e.g. myplace.com/userblog/2009/10/fredspost will redirect to myuserblogplace.com/2009/10/fredspost
2. The bug with the My blogs list in the admin system is now fixed.
3. Problems people had with MU installs in subdirectories should no longer be an issue. e.g. user.myplace.com/wpmu/ will map to myuserplace.com/wpmu/ (note the directory still needs to be in the url).
IF you don't want the front end redirecting, but would like to use the new version then commenting out line 57 (add_action('template_redirect ) will disable that feature.
Thanks for your patience everyone.