Wait a minute, didn't I just read a thread the other day where all kinds of folk are having issues with their Zumo? Is that the real deal, or just few here and there?
Zumo550, 478c, or 2820 are all top of the line GPS units from Garmin. Each has it's own advantages/disadvantages.
I've got a 550 and it works OK - so any reports must be specific to that person...
One thing you MAY need to consider - is it waterproof. So far, there are only two GPS units which are designed for a motorcycle - and therefore ARE waterproof - they are the Garmin Zumo (500 or 550) and the TomTom Rider 2.
Both work off the battery (and have a battery inside for when you are off the bike) - but Garmin is more versatile in what it can talk to - and what can connect to it.
Alan
You missed one - the new Nuvi 500 series is 'supposed' to be' a sort-of poor man's Zumo.
Almost all of Garmin's units were traditionally IPX7 (submersible to a meter for up to 30 minutes) waterproof until they decided to commercialise.
With the singular exception of the Nuvi 500 series, all of the 'i', 'c' and 'Nuvi' models are essentially not intended for NOT ONLY, the moisture laden environment of the motorcycle, but also HIGH VIBRATION and direct sunlight environments . . . even Zumo's screen has issues in direct sunlight - the shiny bezel that the 276 series has is the answer for every situation except one where the sun reflects directly in your eyes (you just shift your head if it happens as you are checking things) - and you couldn't use a shiny bezel if the unit had a touchscreen. The 2000 series tried and fingerprints on your shiny bezel made operation in direct sunlight a challenge sometimes.
The 276 series runs 15-20 hours on it's internal battery and one of the intial criteria was 'the longer the better' before he edited his post. Zumo's lucky to get 3-4 hours with the display turned down. 2820 has no internal battery. It doesn't hurt that if you happen to own a boat, 276 is the hands-down winner, no matter what.
Second: The 276 and it's bretheren were the first 'Motorcycle Friendly' navigators out there, however Zumo and Rider's 'designed for Motorcycle' seems to be analagous to 'problems with quick-release cradle', as both the Rider (1 and 2) and the Zumo (450 and 550) have serious issues the reliability of their cradle designs. Zumo also seems to have power issues - mine sometimes 'goes dead' and that means removing the battery (with an Allan key that I have to carry) to remove the battery and then reinstall it.
As to such issues as routing, all of the units from any one manufacturer now use the same mapping and perform the same routing in their default modes - some (2820 and 276 for example) allow you to place varying emphasis on road types, where Zumo and Nuvi simply have check boxes which can yield some VERY interesting routes if, for example you've told the unit to avoid ferries and it is a long way (like 1000 miles) to get to a bridge to cross the river.
I'm not anti-Zumo or TomTom Rider, per se . . . .
One of Zumo's major claims to fame is that it has a VERY long tracklog.
When I started writing reviews of navigators the standard tracklog (for units with tracklogs - c & I and many Nuvis have no tracklog) were 2000 points, good enough for about 300 'normal' riding miles. 276 was the first with a 10,000 point log and this has slowly become the standard. Zumo goes one farther, by 'rolling' up to 20 full tracklogs into files in memory that can be accessed if you know how - so that would be up to 200,000 points, up to 30,000 miles of 'normal' riding - I had my entire 5000 km ride to Deal's Gap in memory when I got back (it had already been archived to the computer, mind you).
Zumo 550 also is the only navigator I know of that serves as both a Bluetooth client AND a Bluetooth host, allowing you to mate your phone to the device and then couple that onward to an earpiece or into your car's system . . . . so you get to dial from the navigator while using the car's audio system. It's built-in speakerphone is also Garmin's best.
I can go on, but you get the idea.
As to traffic - most people will not be buying the optional traffic receiver for installation on their bikes, if for no other reason that it has a weird form factor though you can get traffic and weather from the XM POD - all of these are subscription services in North America and, at least in my part of the world the traffic service sucks the big one.
Zumo or 276 series or a consumer navigator with a plastic bag. It depends on your specifics.