i think the group management part of openacs is probably one of the few areas where major improvement is necessary. in my site (10.000+ registered users) the default query for the group selection got so slow i had to replace it with a much simpler one. in addition the (unsorted) list of names (without a unique id like email) in the drop-down box is not a good way to select a user with more than 20 registered users. for my (very humble) membership management requirements i wrote 2 new pages where i can search for users and add those that match the query.