Here's the problem I've run into. I go to a website, I see there's no accounts in LastPass, I assume I don't have an account. So I create an account, and then find out later that I signed in with Google or Github originally. So I've started adding fake passwords for these situations just to remind myself that I signed in using a 3rd party account.
It would be nice if LastPass could detect this and record in some way that you created an account on this website using an oauth sign in (you signed into this website with your xxx Google account). With the increase in websites allowing you to sign in with Facebook, Google, etc, I think this is going to become a bigger problem for more people.