I find that Facebook - YouTube and MySpace work perfectly well, all together.
I use YouTube to post samples of my music, which I then add to my MySpace site and use as promotion on Facebook too (and on my main site too, of course).
To me Facebook has been, and is, THE BEST promotion and networking tool of them all, in fact that is the way I landed my composer / Music Library deal (together with TAXI of course). I only wish Facebook had a visitor counter like YouTube and MySpace.
I've had 28.000 visits on the two (YT+MS) but have no idea about FB, except how many signed up as either friends or fans.
I'm not sure really what MS does for me, though it is a pretty good "business card" that people expect you to have (more or less). Also I know, you have to invest some time in the tools, to get any benefits from them. It would be interesting to hear YOUR stories, how you use them all and what you got out of it!??
Oh yeah...I'm on Twitter too, but don't use it much as I really haven't seen 'the light' in that. Have any of you???
I just try to be 'everywhere'....but like I said: Facebook is my main source of personal and promotional network....I have actually sold CD's to people in there who had never heard of me before and probably never would have.