As you guys might know, we're huge fans of Donncha's work, and I think there was much general rejoycing when he released is domain mapping plugin a bit back.
However, we wanted mooooore, and we also wanted to be able to offer you guys a fully supported and actively developed domain mapping plugin that would be updated with every new WP & BP release.
So we decided to take inspiration from Donncha's work and bring you the WPMU DEV Premium Domain Mapping Plugin:
Check it out - it works on subdomains and subdirectories (autodetected), handles cross domain cookie synching, integrates fully with the Supporter plugin and even allows for multiple domain mapping to the one blog.
Have a play and let us know what you think... bugs, feature requests, comments and backslapping all welcome in this thread