Since version 3.0, WordPress integrated multisite code into its core code, so I’ve recently tested setting up a network of sites on a dev environment.
Not so surprisingly it didn’t work, but the generated errors showed that it shouldn’t be very difficult to get it working.
WPMU will require code reorganisation, and enhanced support for upgrading functions.
I’m starting to work on these changes mainly because they will improve the overall quality of PG4WP.
If you are interested in PG4WP support for WPMU and want to help testing, please contact me by leaving a comment here or via the contact form.