Midwest Airlines announced today there will be a fee for the second checked bag. This seems reasonable to me - it gives you a carry-on and one checked piece. I can usually get at least 10 days worth of stuff in that. It'll penalize the heavy heavy travelers without making everyone resort to trying to drag everything on board.
I took the commuter flight between Minneapolis and Milwaukee pretty regularly for the last three years and I'd always try to sit towards the back when picking my seat so I knew there'd be room in the overhead.