I don’t do “social networking” and don’t have either a FaceBook or MySpace account. But MySpace is a lot more useful to me because the majority of the content can be accessed by someone like myself. FaceBook is the walled garden of the Internet, a way of locking information away. To hell with it. If I am looking for information about a musician or band, MySpace is always my first stop. The band’s own website is usually a useless mass of Flash and the songs are hidden and only 30 second snippets.
Livejournal is a blogging site, not what we would now consider “social networking.” Also, it may have been forgotten by Dopers, but it’s hardly languishing in some corner of the Internet where nobody ever goes. LJ is more active than ever.
Is it? I checked on it lately with the intention of rejoining and posting in communities revolving around my interests and there are a bunch of them- but none of them have been posted on in years. Just from the quick look around I had it seems that there are more Russian communities than English ones.
Generally, people who “pimp” themselves out are doing it to get more people to play games like Farmville and Mafia Wars, where the more people you have, the easier they are to play.
IMHO, MySpace fell victim to too many news stories where some teen fell victim to a pedophile they met there. It became a moral panic and many schools and libraries blocked the site to keep those meetings from happening. OTOH, the assumption with Facebook is that you already know the people on your friends list, so meeting up with one of them isn’t as big a deal.
I don’t know about anyone else but I found MySpace very slow to load. I kind of enjoy the ease of Facebook and the sharing between friends I don’t see often is nice. I don’t play the games but many enjoy Mafia Wars and the other games. It is safer for kids but the bullying is getting bad.
I see that Myspace has a Facebook page. 
Myspace always sucked, I’m glad everyone moved on over to Facebook so I could read about everybody’s shitty days at once rather than having to trawl endlessly.
Ah, it’s a fine life.
MySpace, originally for bands, was overrun by high schoolers. It was the in place to be.
Facebook started out for college students and created a base there. Kids from high school would move to Facebook as a sign they’d grown up. In addition, the pages looked better. So Facebook had an older base when they went public.
In addition, Facebook had one advantage: parents. They wanted to see what their kids were doing. So they’d sign up for Facebook. Enough students allowed them to friend that now there was a community of adults on it. It snowballed from there.
It did until I found FlashBlock, and later when they came up with the Lite version option. But, by then, Facebook had already mostly taken over.
I honestly thought that Facebook would eventually institute themes of some sort. Not full control of the page, but at least different colors, if not background images. Instead, they just waited on Myspace to have the same fate as Geocities. People love the freedom to do pages, but the garrishness of the average person’s skills would eventually turn people off to the service.
And, while other social networking sites have popped up, Facebook remained the most popular. It had a large enough base, and the apps idea really took off. Facebook actually has the average person, so niche social networking sites can’t compete.
Even before MySpace was TheGlobe:
I worked for them in their VOIP subsidiary for a few years before it fully collapsed.