I have a 3G that I use on the bike with a RAM Mount medium size Aqua Box with their standard motorcycle handlebar mount. Incidentally, Navigon is an excellent GPS app for use by motorcyclists as it lets one specify an arbitrary number of waypoints and has "scenic" and "motorcycle" routing and speed options, respectively.I use the 3G. Currently looking for a good weather-proof mount.
I see that this thread is half a year old. I'm glad that enough people stated that they use iPhones so that the site admins created an iPhone layout. The iPhone layout comes in handy when looking up a photo on the forum while out wrenching on the V!