I understand that you don't want to bog down the server by allowing a search for the letter "a", but there are valid searches of three letters.
The specific example that leads me to start this thread is "PDF".
Rather than start a new topic before reading the previous discussions, if any, had already covered it, I wanted to read those discussions and see if I still thought the post to be worth cluttering up the SR forums with.
So I suggest lowering the limit to three characters. I'm sure there are reasons against, but there it is.
*off to start a new thread about PDFs*