I stumbled on a cheap handlebar-mounted mirror yesterday ($4) so i thought I'd give it a try. It's got a concave (convex?) mirror so it has a wider angle of view.
So far, there's one big problem. When I look in it, because of the distortion in the mirror, I see this cyclist (me) with an ENORMOUS midsection who looks like he's nine-months pregnant. Yes, I can see behind me as well, but I don't know -- this is NOT motivating!