[Groxx]

I set something like this up myself with a Safari plugin. One thing I learned rather quickly:

nobody searches with capital letters, so hitting the shift key to make a ":" is a pretty big cost. Just use "g <search>", and detect prefixes you know; it's much faster and less awkward to use.

[arvinjoar]

Parang? http://hannesp.se/parang/ The guy who wrote it mentored me when I was a programming noob.

[Groxx]

Same functionality, but I did it with SafariStand. Given how little I used Stand's other features, this probably could've been better :)