It is awesome.
You basically wave your mouse over the page and it highlights what's under the mouse. Then you can hit delete and the element's gone. When you hit save it autogenerates the greasemonkey script to make the change persist. (There are also a bunch of fancier modifications, like changing an element's style with a GUI, but all I really care about is delete...)
My one complaint is that the script it generates only applies to the page, and not the site. They need a "generalize to site" command that just rewrites the URL matching to have a trailing * on it. You can still edit the script manually but that sorta defeats the point of WYSIWYG...