WordPress 3.0 Multisite With Multiple Domains Setup. This article is written for 3.0 alpha, as of the current build on 19th March 2010.
If you ever feel like you want to change the source of the news items on the wordpress dashboard (Not wordpress.com, sorry if I got your hopes up there) here is how to do it.
Restricting the ability to sign up to new wpmu blogs is unfortunate but necessary to get away from all the spam bloggers out there. They make life hell for everyone.