I gave Contribute a test drive the other day. After about an hours worth of tinkering, I'm cautiously optimistic.
I used VPC 5 with an iMac G3 600 so it wasn't a speed demon, but it did allow me to see that it looks like contribute is somehow based around a browser engine (Gecko?) because most of the widgets, panes and messages look like they're straight out of NS6's code. I mean this in a good way. It means it's probably generating good code.
I played only with the basic features - opening, linking, inserting images and tables. Stuff that a receptionist may do (I use this as an example because one of my clients is in this exact situation).
If the end user is moderately experienced with HTML or a WSYWIG editor, then contribute should be the ticket. It's straight-forward, it keeps code reasonably compliant (you can control how it writes style information, what tags not to touch, etc) and works. Mostly. I did get one nasty crash trying to edit a previously unfinished site wizard.
But apart from the rough edges, this may be a very handy tool.