As a longtime backpack carrier (one strap only) I have recently gone the route of the messenger bag based on that earlier thread about the Timbuk2 bags. Got this one (in black, not tartan): Command Messenger - Timbuk2 Bags

Love it so far - big enough to carry around all the junk that seems to accumulate and the don't-have-to-take-laptop-out thing is fantastic. TSA hasn't blinked about it once. It slips easily over the handle of any rolling bag and I have to admit I almost feel like a grown-up without the backpack. But they'll have to tear the parka from my cold, dead hands!!