Firstly, this is an awesome plugin. Really helping many people, I would imagine.
Before domain mapping I visit http://blog1.myWPMUinstall.com/, the plugin works fine, so I can edit content from the front-end at will.
However, as soon as I domain map the blog, I need to visit http://www.blog1.com/ and the plugin then fails to work.
If you need any more information from me, then please don't hesitate to ask! Thanks very much in advance, from a cold and blustery Manchester, England