Sat Nav on a bike? Who'd a thunk it.
I came to Garmin from many years with TomTom. Let me just say that I think the TomTom display is brilliant, but having read about many issues with the Rider 2, I went for the Zumo.
Installation: Piece of cake. I have a BMW R1200GS, bought the official BMW Canbus plug, soldered it to the naked wires on the supplied bike mount, plugged it in to the supplied socked below the headstock, and instantly had a working, intelligent electrical supply to the unit. The RAM mount attached very simply, and, to date, has been rock solid (although DO make sure the unit is correctly seated and clicked in, or it might jump out.
Bluetooth: Can't really comment as I don't habitually use bluetooth (I use a Schuberth C3 and Scala Rider etc are incompatible as the mic booms are too short and the bluetooth "pod" mount then fouls the sun visor mechanism - there is, I understand, a longer mic boom available from Scala, but frankly, life's too short). Worked OK with my Nokia N95 8gb when I tested it in the house, but haven't used it "in anger" though.
Cabling: I routed the cables under the fuel tank, and tucked the three sockets (audio, mic and USB (for the traffic receiver)) under the seat where I could get at them when needed.
Use: So far, excellent. The menu takes a bit of getting used to (remember I've been spoilt by TomTom for years), but is intuitive. Routes are easy to set up, both on the unit and on the PC ready for uploading. The sun can be a bit of a problem, especially when it shines directly on the screen. The unit is (allegedly) non reflective, but washes out in bright sunlight even on maximum brightness.
The voice commands are machine generated and take a bit of getting used to, but generally are informative and accurate. The MP3 player is a useful addition, and my unit currently contains an 8gb Sandisk Ultra micro SD card with lots of music on. The unit is also compatible with Audible audiobooks if you feel the need.
Master volume is much better afer the last firmware upgrade (Jan 09), and I use an utterly bog standard pair of helmet phones I bought off Ebay.
Navigation is as seamless as it can be, and generally accurate. I have found that I've sometimes needed to look at the proposed route, and occasionally use waypoints to get the route I wanted - but then that's a foible of all satnav. The good thing about this unit is that it allows you to do that easily.
It's waterproof - I went through a cloudburst in France. I resembled a drowned rat, as did my luggage, but the Garmin was fine.
Traffic: Connected to the GTM12 FM traffic monitor, traffic updates are generally OK (I routed the cable around the frame and secured it with cable ties, although be warned they're more erratic using the monitor mounted in the car). Have to say I don't use them a huge amount whilst on the bike, but they're helpful in the car.
Updating: Fairly straightforward through My.Garmin.com. You will have to download and install a plug-in for your browser for the unit to be "seen" by the site. I use Firefox and Chrome and have had no problems in Vista.
The map updates are more tricky however. You get one free update with the unit so that you start with the latest map. You will need to connect your unit and download an utterly massive file - 2gb+. Instructions say you will need 13gb free hard drive space - this is absolutely essential as the PC will then "unpack" the file before it processes it and uploads it to the unit. Once you've downloaded the immense file from Garmin (which can take hours and hours - be warned), and you click to open it, don't be surprised if you have to wait in excess of 20 minutes before anything happens - it's the indigestion created by the PC reading the massive file. In Vista you can turn off the security features which speeds things up considerably. Just make sure you don't unplug the unit at any point, or you'll have an expensive paperweight... I allow a good couple of hours for updating the map (which is the "all Europe" one) after downloading the file from Garmin.
Overall: I like it. A lot. Just remember to take it with you when you're on the bike and stop to fuel up!
EDIT : 8 Jan 2011.
Having lived with the unit and used it heavily for a year I am still very impressed. Garmin have revised the update procedure, using an entirely web-driven interface, so no more downloading huge files and trying to open them. That said, I still try to maintain a healthy space on the PC when I do the update. I bought the "Lifetime" maps for the Zumo, which give me updates quarterly.
There were some issue with firmware updates in 2010, that made the unit unstable and likely to suddenly turn itself off. I found a solution was to remove the SD card before doing the update. Since the last update (to 4.0) things have got better.
I also use the Bluetooth now. I don't want to take calls when I'm riding, so don't use a headset, but use a cheap Bluetooth unit for music I bought from Ebay. This lets me hear the route instructions and MP3s without having trailing wires. The downside being the Bluetooth unit is battery operated so I need to carry a charger.
All in all, a good package and a nice unit that (so far) has been reliable other than a few minor firmware induced glitches.