I haven't yet had occasion to do much writing/editing on the N800 -- I've been at home a lot since I got it -- but what I have tried is writing simple html in a text editor. SciTE is my current favourite, but there are several available. I expect this to be my main method of writing on the tablet.

I've tried using Google Docs (not on the N800, obviously) and didn't find it very useful. I can see the attraction if you need to collaborate online, but otherwise I can't imagine myself using it very much. I also looked at ThoughtFree (or something like that) which requires Java, and so is no good to an internet tablet user. It looks like a clone of Word 2002. Pointless.