Never mind. Answered my own question. The "unlimited" part is that you can have as many users in the mySQL database, but you're still limited by what your ISP provides, i.e. no catch-all use.
Would be a great feature. I saw it as part of Hivemail, but I can't seem to get a hold of the people who wrote Hivemail to see if they are still in business.
So any experts out there who can tell me how, using Roundcube, one might implement the use of a catch-all email address? Seems like you could write a script that hits the IMAP server, looks at all the emails in the catch-all and moves them into "sub-inboxes" which users see as their inbox.
One could probably write a script that did this for any webmail client, kind of as a "plug-in", only one that works from the shell/cron level.
Not sure what that would entail in terms of server utilization, but it seems doable. Just don't have time to do it myself
PB