So, why does social networking "work"? Lots of reasons, but I think it mostly boils down to we all love keeping up with our friends, and our friend networks are large webs. We're all getting used to navigating a "web" on the 'net, and applying that to our lives in this manner is natural since our friend networks are really very web-like, too.
Twitter and MySpace are networks that default to a very open manner of publishing info. Unless you lock things, the default is for everyone to see what you post. Facebook, OTOH, defaults everything to locked unless you want to open everything up. I think that's why MySpace appeals to a younger crowd and Facebook a slightly older crowd. But both are similar outside of that, but the open nature of MySpace tends to lend itself to those who want to use it for self-promotion, such as bands that want to get music out there.
Okay, great. That's the state of things currently. What's next? My big problem with all the current social networks is that they own your data. What? How could that be? It's true. There's no way for you to mine what you've posted for info, no way for you to download the information about all your friends, etc. The reason for that? It's simple, really. If someone wanted to build a Facebook clone that was better and that info was available, well, it would be easy for them to write an application that made it easy for you to switch and invite all your friends to do the same!
As it stands now you have to sign up somewhere new and re-enter all your personal information. You have to manually upload any pictures and videos you want. Etc. It would be a huge pain.
Some social networks have embraced others. For example, there is a Facebook application you can install that will let you link Twitter to Facebook. So if you "tweet" something it also appears as a Facebook status update. That's nice, but I'm not sure there's any way to go the other direction (and if you could, and you did both, well, you could create a serious feedback loop!).
Twitter is a huge sub-set of Facebook and MySpace with one exception, the txt-message gateway. With that you can "follow" your friends via txt-message if you like. That is an incredibly handy way to "chat" with friends about their status. For example, if you "follow" your brother via txt and he posts a status update, you get it immediately as a txt-message to your cellphone. If you have the capability on your phone (and most do), you can respond in public or private right from your phone through the normal txt-messaging interface. No need for special applications or clients or browsers or even fast network. Facebook does not have this, and I'm pretty sure MySpace doesn't, either.
Another cool application out there is Google Latitude. With this, you can "publish" your location in real time via your cellphone (if you have a compatible smart-phone such as a Blackberry or iPhone) and your friends can "follow" you with the same application on their phones (or via the web) and know where you are at any given time. This is cool, but not seeming to take off in any serious way yet. The limitation for needing a smart-phone is one problem while the other is the security angle of people not necessarily wanting everyone to know where they are at all times. I think the latter is less of an issue, however, as most people probably don't care if their actual "friends" know where they are and given that the client can be told to stop publishing (or even lie!) at any time.
Another big reason it isn't happening is that Google has no social networking base of customers built (at least not yet) and as such people aren't looking to go have to sign everyone up they know via some other new service. I think if you could do it via Facebook then you'd see a MUCH larger adoption rate.
But on to the "If I were the King of the Internets..." What would I do? I'd create an open source based social networking site. I'd figure out a way to fund it, but it would be owned and governed by the users. The user would own his/her own data. The user interface would be fully configurable. It would include most of the functionality of Facebook, Youtube, Twitter, and Google Latitude all in one. It would be fast, easy, and fun! It might still be funded by advertising, but I remain convinced that advertising done properly isn't evil. Not only is it not evil, but it CAN be done so well that users might, oh, like it! Seriously. I think this model could pull that off, and it would have to as just because users own and govern everything, it still would require a good bit of real money to keep running. It would require serious server hardware, storage, txt-message gateway, and bandwidth...all of which cost real money. Oh, if only I were King...