I really don't like the text entry screen on the 660, separating the alphabet into 3 pieces (A-L, M-X and Y-Z) plus other screens with numbers, and even symbols. Not sure why a keyboard with the full alphabet was not used, the screen is not that much smaller (4.3 vs. my Nuvi 2450 which was 5") to make the argument that it would be too small. I think the old style phones using the keys to type (e.g. 2=ABC) were even easier than this.
One cool thing I have not done yet is using Garmin Express to transfer my favorites from the older unit, that will be very helpful. Have a lot of cool places I've stored over the years and its nice to have that hotel/diner in there when you're looking for a spot.
Paco/Fred,
Glad you got lucky with the GPS like that, I had a GoPro come off my helmet (still not sure how) at Mail Pouch couple years ago on OH555, we retraced our steps looking for it, I was hoping maybe it would reconnect to the blue tooth remote and I'd find it that way. No luck, I've since been more careful and also use a device GoPro provides to prevent the buckle mechanism from opening. $$$$ lessons learned.
Yes GPS mounting is a personal preference like many things, I want mine front and center, both bikes are mounted at/near the stearing head spot. I've never tried it but didn't like the idea of being connected to a handbar area (like on the clip on bolt of a VFR) where it moves around from side to side as the bars move. Mine usually block a bit of the tach/speedo, not a big deal for me. I still have to look down, its not like inside my helmet. Hmm HUD (heads up display) for GPS?
PS Yes the battery door is very sturdy, and takes a lot of force on the latch to open, would be very surprised to see it open on impact, unless like Tosh said the outer case is comprompised.