Hmm . . . . the news of the Nuvi 500/550 is probably important enough to warrant it's own thread, so I've also posted the below in a topic of it's own.
Well, Nuvi 500/550 is 'different', to be certain.
No Text-To-Speech (spoken street names) and such. And, while they have said it is 'Motorcycle Friendly', I suspect it may not be as shock/vibration resistant as Zumo or the 276 . . . at least for the mount - can't tell quite yet because there's no photo, but they DO seem to offer a 'scooter mount'.
But it IS the first waterproof Nuvi out there.
Note that the 500 has no maps on board for Canada or Alaska (they have an SKU for Canada, which likely doesn't have the US roads - like they did with the 200 and 200C), but it does have Topographic maps for the lower 48, PuertoRico and Hawaii on board.
The 550 (same price) includes road maps of Canada and Alaska in exchange for deleting the 'MAD Maps' the 500 comes with. Not certain because it isn't clear from the text, but they may trade off the topo maps for raw elevation data in the 550 . . . They reference elevation data in the description, but the specs state the 550 comes only with road maps installed.
They say it also supports user supplied marine maps and can be operated 'off road', things that Zumo, i, C and the other Nuvis can't . . . . not that you can't tell where you are, but the automotive units will 'lock to road', where the 276 has specific marine support and both 276 and handhelds can be set not to make the roads correction.
You will need to purchase your bike mount and bike power cable separately.
So this is more 'Motorcycle capable', rather than 'Motorcycle ready'. And I'd have to see what the screen looks like in bright sunlight - Zumo's sucks relative to the 276 family's, which is excellent.