I'm a former Nisus Writer user who also uses (or more accurately, used) Word for interchange documents. I'm finding Nisus Express .rtf's are quite acceptable with Windows Word users, which is a great breakthrough. Especially as Nisus Express drives a lot better than Word, and these days pretty much everything works -- bullets, styles,formatting (NE 1 was a bit lacking). Nisus Express is now the best writer's word processor out there. It's fast, it's bullet proof, it's intuitive. Can't understand why it's not showing a full ***** on VT.
The one area which isn't so strong is the graphics handling. For some run of the mill work I like to include graphics and do quick'n'dirty layouts right there in the WP. The old Nisus Writer was excellent in this respect -- NE still only fair, but improvements are coming through all the time.