I usually use it on my Iliad to write down quotes from the book I'm currently reading. For me, it's not...well, it's not the same as pen-and-paper. I do like pen-and-paper.
Have you looked at something like the Lightscribe Pulse Smartpen system? It looks like the best of both worlds, and I know there are some people here (professionals even) who swear by it. I've considered it myself, but I like writing in my Moleskine, and the Smartpen requires special paper (note, Livescribe are enabling, if they haven't done so already, the printing of your own paper with an ordinary printer - that could trip me into the buy-zone).