Vertical, definitely.

Are you volunteering to implement this for us? (please!!)

It can be "easily" done as a user-app through the existing Hijack API; no need for the Cambridge team to do anything here.

(for those who weren't around, I once converted the Hijack menu to "horizontal" format similar to playlists, and it became MUCH MUCH more difficult to use as a result.

Cheers