I like point 0, that the idea doesn't need to be brilliant and unique. A business can be built on making something better, easier or faster. I bet a lot of good ideas are discarded because they aren't seen to be "earth shattering" enough.
I can relate. I have an old high school friend that I used to maintain pretty regular contact with via email since I moved interstate. Early on in the Facebook rise we both had accounts, she still uses her's but I lost interest in it. However, to her online social interaction = facebook and we no longer email each other.
I find Twitter is a bit different though, since it is not like putting your whole life up on a page, it can just be short catchups fairly regularly. Maybe it's better in this respect because it doesn't try to take the place of things like phone calls and email in the way Facebook does.
I agree that this is often glossed over. In fact I can't think of any framework implementation that provides it.
About the best example I can think of is the Atom publishing protocol where a service links to it's publishing URLs and a feed can provide pagination through hyperlinks. But still it is not a particularly sophisticated example, do you know of any others?