I had a Garmin Street Pilot III for the bike and a TomTom3 for the car - both getting a bit long in the tooth, so needed a replacement that would do both jobs.
In the Zumo 550 I have found just the thing. Ease of use is excellent (I never really got on with the TomTom user interface). The MapSource software that comes with it is a little clunky to use at first, but you get used to its quirks. It allows one to manage POIs, routes and favoutites on a PC, and transfer them to the Zumo. There isn't anything comparable for the TomTom GPSs AFAIK.
I now have an all in one solution for the bike - the Zumo replaces the seperate MP3 player and wired phone connection that I used to have, with one device that is wired to my intercom. Now all sources are through one device, the phone connecting automatically through Bluetooth, and it's seamless. The big advantage over the TomTom Rider 2 is that, although it can connect to a Bluetooth headest as well, there are also audio in and out jacks, for better quality (and stereo) music output. You don't have this option with the TT Rider.
In the car, the unit is just as easy to use, and the phone connection can be used for handsfree phone use if you don't already have it. Again you have the wired audio output which you could plag into your car stereo. I wouldn't recommend using the MP3 player through the Zumo's speaker system, as the sound quality is not good enough.
All in all a good bit of kit, and for my own personal requirements, beats the TomTom Rider2 hands down.