To summerize: It is very difficult to determine if a download was illegal or not. As said, downloading mp3 of CDs you own is legal, or it as least not clearly illegal.
Since this area is so grey, this is the reason why the RIAA concentrates on uploaders. Since there is nothing that makes an upload legal unless you somehow spefically checked the one you make a mp3 for has bought the CD. That is why the RIAA connects to your shareware software downloads stuff, and then claims at the court, that they had no right to download it from you, so you must have commited an illegal act
