I actually disagree with DJStitch somewhat. There is generally no point in networks any more. The only reason to join one is that some have agreements with certain sites and services that mean you gain access to them by being part of the network. This is only worth it if you actually want to use them and can't really afford it yourself.
When I was with Fullscreen, those signed to the network got nothing - they were rubbish with their support, they offered no services, but they took a percentage of my ad revenue (admittedly pence). Now I'm with Maker I get access to a wealth of music and sound effects from Epidemic for free, and I can use Epoxy - a central hub to see interactions I've had on YouTube, Twitter, Facebook, etc, and you can make little videos to post. Just depends what you're after.
P.S. I am with DJStitch on one thing (from another thread) - take off Caps Lock, bud