Take units in one locale and change them to another, in place (Chrome).
When I'm reading an article or recipe, I'm too lazy to take on the extra cognitive burden of remembering how to convert things or switching context to look them up.
So, this plugin just replaces stuff in the page, with a title-text showing the original text.
http://htmlpreview.github.com/?http://raw.github.com/stringfellow/unitify/master/test.html
Fork it, test it using the test.html:
unitify $ python -m SimpleHTTPServer
Then submit a pull request.