Been using the Nuvi 780 on my bike (and occasionally in car) since last November. Just returned from a 3k+ mile trip into Nova Scotia relying sololy on the Nuvi and had no issues. With only an open framed RAM mount, it rained considerably, but the clear plastic glad baggie and tie wrap worked well. My friends 2720 is water proof and was easier to manage when it came time to 'waterproof' mine. Nevertheless, the Nuvi worked well.
I am having BT issues with wind noise in the mic. However, I'm beginning to think it's my Shoie Multitec helmet, which is loud.
Over all, for the price point, it is very capable. If there is a concern for it's ruggability, then purchase the extended warranty as an inexpensive investment.
Hope this helps.