Wrttn.me is a notepad for the web that you can embed on any page and style with custom CSS.
Wrttn.me supports more than just plain text too. You can use markdown, textile and HTML in your pad as well. A public URL is available for sharing, but you can also post directly to Facebook, Twitter and Google with a few clicks. Notepads support commenting too, so sharing can be a way to solicit feedback.