I've just joined this Geocashing and have yet to get my first one.
But on the subject of GPS on a motorcycle i use an Emap with a RAM mount, which I imported from the US but you can get them here now, Cut's out all the vibration and the positioning is much higher so you can GLANCE and ride, ( I have done on a ride to Bavaria)
well worth it for only about £30., You also get them for other GPS, on the RAM site you get ones for Hand Guns (AHHHH), well it is a US made item.....