Has it reduced piracy in a true sense? I would think so.
It it helping artists? Not really. the artists get a tiny payment per play, it's miniscule. It's legitimate only in the sense the artist gets paid, but not by how much.
I stream and use digital downloads all the time, I buy CDs of albums I enjoy and they get added to the collection to gather dust - but I still adore having that collection because no matter what happens I still have those CDs, I still have access to the music if my laptop fails or my ipod breaks or the cloud/server/account fails.
Yesterday don't mean SHIT.