I actually started writing an article on this, but it's been sidetracked with travel and other stuff. However I do mean to get back to it at some point.
In the meantime, Jamie Thomson went ahead and wrote a nice entry on Business Intelligence, what is it and what is it not?. Jamie does a good job of breaking up some myths and then giving a short explanation of what it means from the practical world of someone working on it daily. Highly recommended.