This is probably the biggest single change we've shipped to the site since we started (until today the only way to sign in was using Twitter - as of now you can sign in with LinkedIn or create an account with an email address and password as well).
It turns out handling multiple social networks is pretty tricky! We've had to implement full account merging, so if someone signs in with LinkedIn and then tries to associate a Twitter account that they've already got an account for we offer them a merge screen.
Since we have HTML5 and iOS mobile apps already out there we also had to coordinate a switch-over for them to having an account picker signin screen. We shipped the mechanism for doing this a couple of months ago.
It turns out handling multiple social networks is pretty tricky! We've had to implement full account merging, so if someone signs in with LinkedIn and then tries to associate a Twitter account that they've already got an account for we offer them a merge screen.
Since we have HTML5 and iOS mobile apps already out there we also had to coordinate a switch-over for them to having an account picker signin screen. We shipped the mechanism for doing this a couple of months ago.