Wouldn't be cool if you had a device that told you where to ride your bike? Instead of cue sheets, just this really clever little computer that kept you from getting lost?
I purchased the Garmin Edge 305 back in 2006 hoping that it would be just that. I wanted in-car GPS functionality, as well as speed, cadence, and heart rate. I found, quickly, that you can want whatever you want, but you can only do so much to work around a poor product and poor software.
The Edge 305 is not customizable in the way I want. I want to be able to upload routes and follow them easily. I don't want to worry about the pathetically small memory of the device getting filled. I wish I didn't have to work this hard to figure this out. I've been fighting this stupid little device for going on two years now, and there is no elegant way of getting routes onto it, short of wiping its memory every time. It's designed for repetition of a few routes, not touring.
An in-car GPS works well enough, but it's not designed for a bicycle. It won't tell you speed, cadence and heart rate the way that the Edge 305 does, and it won't mount on your handlebars or withstand a rain shower, but at least it works.
Garmin is releasing the Edge 705 later this spring. If that device were to support proper routing, and give me speed, cadence, and heart rate, AND be able to listen to my PowerTap SL 2.4 power meter, I would be quite pleased. Time will tell.
Maybe I should just give this all up and stick to paper cue sheets.