> But if it doesn't, and I want to impress people by showing that I listen to it, and there's no way to do that on Ping except by buying it from iTunes.
Actually, there is. In my opinion it is a very bad way to do so, but you browse on the ITMS to the music you want, click on the down arrow and click on Post. Then you can add a message and it will be appear on your Profile.
But as I said in my comment[1], they should have made all that accessible from within my library!