As someone who regularly makes journeys with a Garmin Nuvi 300 sucker-cupped to his windscreen, I'm half-pleased and half-dismayed to see this new, sexy widescreen Nuvi 660. It's dripping with features my old model just wishes it had; Bluetooth 2.0 to act as a hands-free kit with your cellphone; an FM transmitter to enable wire-free connections to any radio... all of a sudden the mp3 functionality sounds like it might actually get used.
What's the same is the ridiculously straightforward interface, that makes picking out and storing addresses easy as a particularly easy pie, a bumper collection of Points of Interest (POIs) accessed through chunky, finger-jabbable icons, a sizeable chunk of free on-board memory for your own use and SD expansion. I also know for a fact that Garmin regularly release firmware upgrades adding functionality and tweaking usability, plus they're very responsive to customer suggestions and queries.
Would I recommend the 660? For an estimated $1000 you'd have to really really have trouble finding your way around and want those extra features.