I think someone on here did a very comprehensive back to back comparison of the Zumo v Tom Tom Rider. Just search on 'Zumo'.
Also excellent website dedicated to Zumo owners:
http://www.zumoforums.com/index.php
I have just fitted mine and still a novice in the sat nav field. Your biggest problem with the Zumo after wiring is how to connect to the helmet as they do not supply a headset. I have just purchased a Bluetooth receiver with bud earplugs as I like some reduction in wind noise and normally wear earplugs. Yet to try the rig out on the bike but works on the sofa!
Plenty of options available. If you go hardwired to the something like Autocom you can have the phone, intercom, music, sat nav, two way radio etc. Personally I like to focus on my riding on with little distraction.