Hrm.. that could be tough. The biggest issue is the size abilities of the U_Groups field in the users table.
Groups are stored like this '-1-2-3-4-5-6-' etc.... so there would be a finite number of groups that a user could be assigned to. Likewise in the Board table, if you needed to excede the field size, you'd have to alter the field types in the database, so that they wouldn't get truncated.
