Perl has a concept called “DWIM” (do what I mean). Greg McCarroll has prototyped a idea that he calls “SWIM” (search what I mean) where he monitors the speed that you type words in a Google search box and automatically quotes words that seem to have been typed together.
There’s a fuller explanation in his blog and you can also play with the prototype.
Now we just need someone to turn it into a Greasemonkey script.