Interesting thread...
I have a Garmin 2610 (which by it's size probably damps out a lot of the vibrations itself - it is the size of a brick!). However, it is also a fantastic GPS for on-bike use, so I don't care! - Simple, intuitive and above all robust...
I use a RAM cradle and short arm, with the ball connector on the handlebars between the bar clamps - no problems - it's easy to reach the touch screen, and fills in the 'gap' between the instrument panel and the bars.
Perhaps the Tourtech cradle will help in the instances described above?, but I tried their version for the 2610 last year (when it was fitted to my XR650) and the standard rubber one did nothing, while the foam pad MvG version was excellent up to 50mph, when it would start to vibrate so badly (on the foam pads) that you couldn't read the screen!
Perhaps their versions for other (smaller/lighter) GPS units are better in that respect? - just be aware before you spend
a lot of money... personally I would recommend the RAM system every time...
xxx