If it doesn't take off as a service but stays as a looming threat to Facebook, especially being open source and impossible to entirely kill, it'll still be worth it, though granted still a disappointment.
You could get a basic, working social network built for a few hundred bucks, but that wouldn't make it a threat to Facebook. And Diaspora won't be one either, unless they've got a trick up their sleeve.
The only thing that is a threat to Facebook is something that causes them to start hemorrhaging users. But face it, when the average person logs in to Facebook they have new stuff to look at it and people to communicate with. But if they signup and login to Diaspora, there just won't be as much activity, if any. So the average person will go back to Facebook, and stay there, until all of his/her friends move to Diaspora. But they won't, for the same reason. It's just not going to happen unless there is some fundamental change.
The reason Facebook gained users so fast was because they generated incredible amount of buzz by making it exclusive and lauching it at Harvard. If I were diaspora, I would follow the exact same launch plan. However, from what they're saying it sounds like this won't be the plan.
So when they launch they'll have a bunch of hacker types come signup and check it out, and they'll possibly even invite their friends. And a few friends may even join. But those friends (normals) will go back to Facebook simply because there's more stuff to look at and more people to talk with. And that will be the end.
However, that doesn't mean people won't end up using both. Free software types will gravitate to something like Diaspora and so will their community friends. You may not get every community off of facebook, but you may get a few.
I can see political communities moving to Diaspora, I can see technical communities gravitating/dual use with twitter... No, it will probably never be as big as either, but that doesn't mean it won't fill a niche.
The sad thing is that full-time individual adoption of a social network requires mass adoption the social network. That is to say, not having everybody and their grandma on Diaspora will be a fairly big downside compared to Facebook.
As for having both, personally, I'm looking for a way to not use Facebook at all and still get the benefits. Right now I just don't use my Facebook account. Having Diaspora would be a small improvement, but if it's a lukewarm thing, my friends will be more active on Facebook, and won't be that active on Diaspora.
Maybe there'll be a Diaspora app for Facebook, ha. I'm not familiar with Facebook, is there a way to do this without giving Facebook all the data you were trying to hide from it in the first place?
Actually, another thing I just thought of. If we could get people to just create the Diaspora accounts, and just connect it to their Twitter, Flickr, and so on, it may be enough. The updates will happen automatically. I'll still be able to browse my friends' pages, which will be updated without them thinking about it.
