There are several things that contribute to mirror vibration. First, it depends on the length of the mirror stems and the shape of the stems. If you've got long stems that rise high (vertically) above the handlebars, then you're headed for a vibration problem. The reflected image in your mirrors is gonna' look like a UFO on drugs! Look around and see if you can replace the stems with a design that only rises vertically by 3-4 inches, then turns out and runs a longer distance horizontally. That helps.
If you want to keep your existing mirrors and stems, you can try re-doing the mirror mount with some rubber and electrical tape inside the mount. Basically, you are creating your own vibration isolator. Or alternatively, check out that link that someone posted for the "Vibranator" that installs inside your handlebars - looks like a pretty clever design.
I use the mirrors a lot - because I ride in congested traffic in LA.
But I still agree with one of the comments above - you gotta' turn your head and check those lanes beside you. Mirrors won't save you from insane cages. If you're riding beside a car in a nearby lane ... always stay out of the "death zone". That is the region of physical overlap where if the cage suddenly pulls over into your lane - some part of his vehicle will clip your bike. Accelerate through that zone, then re-set to cruising speed.
dT
