You can check if it's charging by using Android System Info (from the Market - it's free and can be installed if rooted). It has a neat battery use screen (as well as many other info screens). It will show the battery percentage and charge state.

I've found than if WiFi is off (as when the NC sleeps) even a 500 ma power supply will fully charge the NC overnight. I use my Blackberry phone charger (with the cable that it came with) and that way I only have to carry one charger when traveling.

I even use it for charging while playing music/videos or reading and even though it doesn't increase charge it does slow down the rate of usage.