Great points. Here's my two cents.
I bought a N800 because it was the right hardware for what I wanted to do. I needed something I could write on, something I could instant message on occasionally, and something that was light enough and small enough to have on me all the time. Some phones are good for messaging, some notebooks are good for writing, but the N800 brought it together for me.
Having Maemo, the open source OS, come specially developed for the N800 was a super plus because it offered me a lot more flexibility. True, a lot of what's out there is the standard issue FOSS apps -- but that's the point. I've run SSH sessions from my N800 to diagnose headless server issues, for crying out loud.
The rest of the time, I write on it, do some twitter, and keep it comfortably out of the way but close at hand. It's a brilliant device, Nokia made some great hardware choices, but they're not in the software biz. FOSS only helps make it better, and was a solid development choice.