One thing I've noticed: when no user in the room can provide a drum track, jamming becomes very difficult: people tend to ignore the built-in metronome, and soon everyone starts improvising their own riff in their own tempo (at least until a very committed bass player comes up with a convincing riff

In these situations it would be cool if the jammr server could provide some basic drum tracks (selectable from a menu in the jammr client, maybe extending the current “voting” feature?). Or, if this is not feasible on the server side, maybe it could be implemented as an extension / plugin for the jammr client: I'm pretty sure there are repositories with drum tracks available on the web under free licenses (Creative Commons etc).

Thanks for the suggestion!