I'm having decent luck with a blackburn velcro-to-the-helmet model right now. Problems with these sometimes are that the pivots (just a plastic ball/socket joint) wear down and it'll bounce out of adjustment all the time. A little superglue will aleviate the problem, but the mirrors are so cheap that it's no problem just to pick up a new one. I'd be curious about homemade ones. I usually have a visor on my helmet and tuck the mirror up close to it so as to be as inconspicuous as possible since I already tend to look like a cyborg with a helmet-mounted light and its wire.
I've caught plenty of flack from buddies at the shop I worked at for having a mirror. One told me that he'd rip it off and stomp on it if I showed up to a ride wearing it.... "Why can't you just look behind you?" Because I want to know what's happening behind me all the time (like every 10 seconds), not just when I'm about to cut into traffic to make a left hand turn or whatever. A quick glance in the mirror is far easier and faster (for me) than turning my head. Plus I'm often wearing fairly narrow prescription glasses, which really cuts down on my peripheral vision, so I'd really have to crank my head around to see anything. I'm biking mostly in the city too, so higher ambient noise tends to drown out aural cues you'd normally pick up elsewhere, like in small towns and the country.
My general philosophy is that I am profoundly more interested in my own well-being than strangers passing in their cars are, thus I depend on myself -- not them -- to steer clear of disaster (yet strangely I would never touch a reflector vest....

) . There are plenty of distractions for drivers and I don't want to end up in the hospital (or worse) as a result of a few seconds their carelessness. Is it a perfect 100% great system? Not nearly, and it doesn't lull me into a false sense of security. I realize the risks (mostly), take risks aplenty, but I minimize them when possible by riding as defensively as possible.. After a few years of having a mirror, I've seen some sobering stuff happen behind me that could have been potentially dangerous.
SpinWeelz: If the head-tuck works for you, good on ya. Some people don't have the range of motion, coordination or peripheral vision for it. I do it from time to time because I think a person should be able to use any and all methods to get the job done, but I prefer the mirror anyway just because I use it so often (gotta be on guard in the city) and it works well for me.
Tim T.: 180 degrees? Maybe you should rethink your "geometry"

It doesn't take that extreme a head movement to look back.