Another comment in this discussion admitted of that in passing, pointing out their real strengths are in sharing, etc., but MS's Live Office is also very strong in sharing. In fact, in simultaneous editing, it surpasses even Google Docs.
(You can try out the Live Office at http://skydrive.live.com/acceptpreview.aspx/.documents?aobrp... or at least you could a couple of weeks ago; don't know if they're accepting new previewers.)
I don't mean to bash Google or Zoho and praise MS, but this is a serious issue.
Will anyone step up to the plate with a serious browser-based document editor? Perhaps none of the solutions that rely on the in-browser editing will ever be any good. I've been tempted to write something more serious with Cappucino, but that's a pretty high hill to climb...