The usergroups are a very elegant idea, which I think is also elegantly integrated with the shares. However they can serve more purposes than just download permissions and priorities. It would be nice if I could split the user list by group, so that all buddies that are in a specific group are shown on top while all other are shown at the bottom.
(Off-topic: I've made several comments and feature requests by now. This is a compliment: I think SoulseekQt is worth the effort of giving this much feedback!)