Although it has the same name as the old "Broker" functionality, that has sense been moved elsewhere, this user-created Utility helps to expand upon the item tooltip information to show a larger picture of the supply and demand side of things and more.
For those who are really trying to squeeze out every Copper from your markets, and you like what Auc-Utility-Broker does, then you may be interested in http://wowinterface.com/downloads/info12911-MarketWatcher.html which is a completely separate AddOn.
It is not intended to replace Auctioneer, or even Auc-Util-Broker, but will allow you to track minutia of specific items. The resulting files are quite large, so be sure you only add items to its tracking that you already have a decent idea will sell.
So, use Auctioneer, along with Auc-Utility-Broker, if you like, to find general trends, and then add a few dozen items with which you are already relatively happy to MarketWatcher and go from there.