I haven't mounted on my bike, but I have used my Garmin 60CSx many many times while riding. I usually throw it in a rear jersey pocket and take off. I find it interesting to see where I've been, what it thinks of my speeds and elevation changes, etc.
/begin gps product plug
One great thing about the 60CSx is that it has a MicroSD expandable memory outlet. This means if you throw down an extra $100 for a SanDisk 2GB MicroSD card you can get the entire US map will all local points of interest on a single GPS with no loading/unloading of maps each time you go someplace different! Pretty cool!
/end gps product plug
I believe the Garmin 60CSx does have a handle bar mount but to me mounting something that big on my bars would be too distracting.