(This page is incomplete - please feel free to correct and expand! It still needs information on: how to purchase Patron accounts; maximum number of categories, content pages, files, and friends that each account level can have.)
There are at least four account levels on Tabulas. From most to least common, they are: registered, patron, beta, and administrator.
This is the most common account level. Registered accounts have access to most features: they can post journal entries, upload images to their gallery, edit their profile, create content pages, add other users to their friends list, and add links to their links page.
As of March 29, 2006, a Registered account may upload up to 150 images to their gallery. (link)
As of March 22, 2006, a Registered account may upload up to 8 usericons. (link)
Registered accounts are free of charge.
Patron accounts have a few features that registered accounts don't, usually because making these features available to everyone would overwork the server or cause Tabulas to lose money.
In addition to all the registered-level features, Patron accounts may also upload files, edit an online mixtape, and view linkbacks and related entries.
As of March 29, 2006, a Patron account may upload up to 1,000 images to their gallery. (link)
As of March 22, 2006, a Patron account may upload up to 128 usericons. (link)
Patron accounts cost money. As of January 18, 2006, a Patron accounts costs $28/year, $16/six months or $9/three months (link).
In Roy's own words:
"Beta accounts were people who signed up during the first few months of Tabulas. They were also granted out as gifts to people who helped out with the Tabulas community as gifts from me. They are permanent patron accounts." (link)