For the quickstart sample, take a close look at the SimpleConnectionSignUp (https://github.com/SpringSource/spri...ionSignUp.java) class. Right now it doesn't do anything terribly interesting. But you could use the connection given to implicitly create an account on your app. Or you could use it to create a for-this-session User and sign them in (which is essentially what the SimpleSignInAdapter does in this example).
I can't speak to why other projects are abandoned (or put on hold). But yes, there are a handful of attempts to create a tighter integration between Spring Security and Spring Social. And yes, there is a plan to officially bring that into Spring Social in the 1.1.0 release (currently underway, but no date for delivery yet).
Spring Social Project Lead