Having installed and played with the plugin over the past week I've got to say that one great undocumented feature is the ability to (shut your eyes Andrea) go to your host and say "HA! vhost can't be set up correctly or else blah would occur!"
The deal breaker for me is the out-of-the-box cookie issue with integrated fora e.g. bbPress. I had hoped to have one forum to rule them all by casing the blogid (or other identifier) in bbPress's config before specifying that particular blog's user table and cookie domain but the wheels fell off... (time alloted)
Apparently git'Rdone doesn't include integration and testing.
The plugin worked as advertised for me (v4).
WPMu 1.5.1 subdomain method
Apache 2x
PHP 5x
MySQL 5x
Some hosts use "a tool" that appends new serveralias directives to the conf file. That's fine as long as they go in and manually move your parked domain info' above/before the primary domain's wildcard glob. Doing what they always do is not the same as doing it correctly for this setup... Hey, my host is gracious enough to permit this, stuff, until someone signs up and I get kicked off...
Plugin: Very niiice.