Receptional Andy at WebmasterWorld has shared a great guide with us about how punctuation impacts search results in Google. For example, key|word is like a boolean operator and tells Google that you're looking to search for either "key" or "word." On the other hand, a word like key~word triggers the Google related: search and gives you both "key" and "word" but also similar search results.
There are a plethora of different results that you can find by using a variety of punctuation in your searches, and it's very interesting to see how Google weighs them all. Andy goes into the different types of keywords, such as key-word, key"word, key*word, and others.
I won't detract from the brilliance of that thread, so head on over to the WebmasteWorld thread for the additional tidbits and the results of Andy's research.