Well, its downright illegal and unfair for the artistes involved.. Imagine everyone downloaded from forums and forget about buying Ayu's CDs.. She would never ever sell much or even get into Oricon.
Downloads are for evaluation only, don't burn them and sell them. Just listen to them and purchase them if you like it. Its a sin to keep the downloads you like and listen to them and ignore the prospects of buying the stuff..
An artist called M.I.A. (maybe somebody knows her here..) whose album got leaked all over the internet even made a mixtape called "Piracy Funds Terrorism".. Dont know how true that is though..
This should be in enquiries.. (-.-)