I have some of my music up on my MySpace page. People come and listen, and sometimes leave comments. I have not set up anything to make sales there.
I have neglected my MySpace page, and it seemed that MySpace went through a bit of a lull in popularity, as Facebook came to the fore. But MySpace is likely to have a resurgence of interest.
I just received a notice that there is something called the Facebook and MySpace Mashup, that merges some of one's Facebook content with their MySpace profile. I am going to watch for developments before trying it out, but it could have some benefits. MySpace is also going to a new format on 11/29/10. I hope it is attractive and easy to navigate.
You can arrange to have your MySpace, Facebook, Twitter, and some other online hubs linked together, so that if you post on one, it appears on all of them. This can be helpful for promoting yourself as a musician, or anything else.