One of the main problems with the Zumo over the 60c range is that if you have uploaded a route in the Zumo and you aren't starting from the beginning of the route it will keep trying to send you back to the beginning of the route to start the route from the beginning. Fine if that's what you want to do but with the 60C range you can easily manipulate the route by inserting via points and taking off and following the route from where you intersect it. The 60c range is designed for outdoor activities and it does turn by turn road navigation as well, The Zumo is designed for turn by turn navigation and doesn't do the hiking , trekking, off road stuff as well as the 60C range.
If you want a go anywhere , do anything kind of unit that doesn't have a sexy female voice , MP3 player, blue tooth phone connection and other gadgets then the 60C range are very fine capable all round GPS navigation units. If you want the whilstles and bells and aren't likely to do much off piste dirty navigating the the Zumo is an excellent bit of kit. I have a friend who uses one for road trips but any time we go off road , out comes his old GPSV with 19mb of memory because it's much better for non-road based navigating and track following than the road biased Zumo.
I have a 60C myself with 56mb of memory and it's brilliant on the bike. It's well made, waterproof and does more than I need - of course I'd like more internal memory but it's never been a real problem yet travelling around Europe.

__________________
...on the road to nowhere...

Biking roads by bikers for bikers www.bestbikingroads.com