Thank you for all your effort you put into this plugin! It's really great! Anyway, I have found some issues that came with the unlinking functionality:
1. If I want to unlink my Google account and click on the unlink-button for the first time, I get to the account selection page of Google (for users with multiple Google accounts) and after I selected the correct account, I get redirected back to my profile, but nothing happened, the account is still linked (not even an error-message). When I click on the unlink button again, it works.
2. It seems like you redirect to the social network when the unlinking button is clicked. Wouldn't it be enough to just remove the link-data from the database? As the user has to be logged in for that action, there is no need for further verification.
3. It seems like your "redirect" parameter is no longer working. I always get redirected to the home page, after I successfully linked or unlinked an account. (But only for the "link account" and "unlink account" links in the profile. The login buttons I added to my comment form work fine.)
4. The unlink function does not work for Twitter, as you forgot to add
&action=unlink to the url.
Sorry for mixing up Google/Facebook/Twitter, but I think that having all unlinking-issues in one post is better.