Using Greasemonkey again, we were able to Wikiwygify wikipedia.org!

You can try it at home:

1. Use Firefox
2. Install Greasemonkey 0.6.4
3. Install this user script
4. Visit a Wikipedia page
5. Try clicking the [Edit] section links.

Note: This is just a demo. The 'Save' button doesn't save changes to the server yet. But you can save them to the browser. All changes will be lost when you leave the page.

Enjoy! Viva Greasemonkey!

Screenshots: