You're kind of missing the point. Facebook *is* the "cloud" that replaces e-mail, forums, blogs, etc. (at least for a lot of people - I have an account but never use it, but do use the other options you mention). It's accessible from any device, anywhere, and if your friends and family are all using it too then you can handle essentially all of your correspondence on it. In two years everybody will certainly not be hosting their own communication systems.
Why would people who use it in that way - which, again, is not me but it is a lot of people - want to look for "other means" to do these things, when it's all already in one place?
We geeks will do our own thing. We tend to form connections differently, and more regularly have discussions with strangers (on the internet, like we're doing now). But even a lot of geeks see the appeal of all the people they care about being in one place.
This isn't to say that there isn't a better solution, in theory. A cloud-based decentralized system not controlled by a megacorp would be ideal - but it has to have all the features Facebook has and more, and it has to be seamless across any device like Facebook is. I think this is the idea behind Diaspora, but excepting some major event (like Facebook and Google Plus and Myspace and whatever else all suddenly disappearing, or forced integration into Windows maybe) Diaspora is probably going to remain a Linux-like niche.