I have had the Garmin Zumo 660 for about 5 years. Feature for feature, their other models don't compare. Several friends have other Garmin models, because it's cheaper, as well as the TomTom and Magellan.
The Zumo 660 has built in bluetooth, MP3 player, computer routing, extremely easy snap-on/off from the sturdy cradle it comes with, it recognizes the motorcycle vs. car cradle and comes with both, integration with both my Sena SMH10 and Blackberry phone are seamless, gives me avg speed, elevation, compass direction, top speed, the posted speed limit, time and distance to destination, lane guidance, and quite a few other features I'm sure I missed. It automagically connects to both the Sena and Blackberry on powerup. I can just press "phone" on the Zumo and I get the entire list of contacts on the phone.
I ride about 20-25,000 miles per year. I plan 3,000+ mile rides with plenty of interesting stops on my computer and load it on the Zumo. When I'm out in a completely strange area of the country and hungry, it's cool that I can search for a restaurant that sounds interesting and can just press the phone number on the Zumo and it connects me. I ask the restaurant a few choice questions, then press "go" and it takes me there.
My Zumo 660 has been reliable for over 100,000 miles and I continue to use it. Being IPX7 rated waterproof is just one feature.
P.S. - No I don't work for Garmin, nor have anything to do with their company. Just a Zumo fan.