Kim of Emergiblog explains nicely why you should support Open Access publishing:
The Public Library of Science:
You are writing a paper. You need to do some research, so you google your topic.
Ah ha! There it is! The perfect article for your paper. The abstract is right in front of you, but you must go to the actual journal for the full text.
Hmmm...you can access the full text of the article, but you must pay to do it! Anywhere from nine dollars to almost thirty dollars for twenty-four hour access.
"No way", you say! "I have access to my university's online library, I'll just go there and look it up for free!"
Except the journal isn't in the online database or it has to physically come from another library, and you happen to live two thousand miles away from your "campus".
Reluctantly, you pay for access to the article. Or not....