I've so far only used it for Digg, but honestly I like it better than the "share this" links you find elsewhere.
How it works:
A text link remains on the right of the screen and when you click it, the menu opens up. Click it again, and it closes.
* Includes Diigo which is often left to the wayside, but also includes many others.
* Is non-intrusive.
* While it is un-intrusive, the text link is still a bit large (for smaller screens) and from what I can tell, it cannot be resized.
* You cannot hide the text link either.
All in all it works as promised. If I had a wish list item, it would be to select a size as well as a way to hide it altogether.