It's mentioned through a few posts, but we do need to work up a full license. Sorry about that.
The purchase will get you full upgrades throughout the lifetime of Joomla 1.5. With the new user system of Joomla 1.6, we're still investigating our course of action there, but we still don't have all the information we need about it to determine the amount of effort it will take to re-do the user creation functionality..