I might have a different perspective than most, but I think csv as a raw access method is far better than any structured format.
The contract on what is transfered or how it's mapped in your csv is developer to developer and not in code.
This is a problem and also a benefit.
As long as both systems are designed to read and write the csv correctly(there in also the problem of verification), csv works flawlessly and retains its simplicity.
My honest opinion is, We should consider the Ycombinator demographic that is going to go ever younger.
There are going to be younger programmers, what do we do about them?
I have learned a lot from the articles here, but at the cost of being burnt most times, we need a handle or method to make Ycombinator accesible for new learners. Ask HN Noob?
Haven't heard about LinkedIn trying to login using social media, but LinkedIn has a feature that does contact import.
LinkedIn asks me to sync my contact/address book information from another source. After the import runs they show you connections that match your contacts sometimes in the connections tab.