Nice idea and the implementation seems good. I am tempted to use this on some of my sites.

Some questions:

a) How does it work? Lets say I have a recipe site and a visitor arrives from Google having searched for "steak". How do you find related articles on my site?

b) What if my site isn't indexed? (e.g. new, blocked etc)

c) The widget has 8 actions (links/buttons etc). 2 of them point to my site and 6 to yours! I would prefer something like 7 to mine and 1 to yours :)

d) Certainly add some options. The "Looking for more on", "Or try a new search" and the 3 related keywords should be optional.

e) The 480px is very limiting. I can't put that in a sidebar it has to go to the main area

f) The site copy needs a redo. I could not easily grasp what it does, how it works etc.

Great work overall - I hope my suggestions are well taken!