Puppy Linux seems fine in that it is quick (particularly Gmail opens much faster here than it does in Opera on Ubuntu.
Youtube videos play fine although it does seem just a bit jerky like the FPS rate is too slow.
I haven't yet tried to play music files on it but there are media players and, if Youtube works with sound , no reason why music shouldn't play.
It connects quickly to the internet on clicking the icon but doesn't, for some reason, connect on start-up.
It, of course, doesn't have any of the fancy stuff like Compiz-Fusion or AWN but if ll you want is occasional light browsing, then I don't think you'll have a problem with Puppy.
However, I haven't yet tried the forum which, to me, is a very important ingredient in the OS mix.