Have been using a tomtom for 3 years on the mobile phone and have just bought a garmin 550 traffic for the bike (and the car).
The garmin recalculates a lot faster than the tomtom. The guiding is a lot clearer and the 550 will do a million more things than the tomtom. Especially if you wanna use it for the bike you will be very impressed. It is waterproof, you can use it with gloves, you can load mp3s, you can go for a ride and then come home and record the route you took and go for it again at a later date. The screen is much better and it comes with 2 cradles - 1 for the car and 1 for the bike.
good forum for the zumo is
www.zumoforums.com
cheapest I have found the zumo with traffic is 389 from mncgroup (use google)