Pardot has just rolled out (see what I did there?) the abilities to define custom user roles. Custom roles are included in Ultimate Edition accounts (or as an add-on to Enterprise Edition accounts).
For full documentation on how these are used, take a look at the Custom Roles article in the knowledge base.
Folders with asset permissions are coming soon. Folders will be available to all accounts for organizing content. The ability to set permissions on folders will be available to Ultimate Edition accounts (and Enterprise Edition accounts that add roles/permissions as an upgrade).