It'd be nice if there was something you could do in game for those times when you just want to kill 15 mins or so, not necessarily sit down for a bona fide "gaming session". There's some stuff you can do - manage your AH, tidy your bank and inventory, crunch your crafting, maybe go kill a couple bosses on Kobold Island for chests or run a short challenge if you want - but there really isn't a lot of actual "drop in, drop out" kind of content. When you factor in login times, and especially city travel times when you cant Teleport, that can add to your time total in-game too.
What I'd like to see is some "impulse" content, something centrally located (HoH maybe? Marketplace/ES?) that you can just drop in, get right into the action, and complete in 5-10 mins or so, for some modest content like a chest, a smidgen of XP, etc. Doesn't have to be competitive with actual questing in terms of rewards, just for a little fun and change of pace. Maybe just a random boss fight, or a quick gauntlet, or "kill 100 kobolds in 10 mins" or something.