I'm testing this plugin and it seems to work very well, but there is one small glitch.
I use ReCaptcha on my site and when I login via twitter/fb, it redirects me back to my blog post, but the reCaptcha is gone.
When the page is refreshed the reCaptchs comes back, but the initial logged-in page load its missing.
Not a biggy, but people don't like seeing the error message when they first post
UPDATE: Theres a setting in reCaptcha not to show for people that are logged in.
Although the user can see their profile when authenticated through Twitter, they're not seen as being logged into WP(?) and so the Captcha code still shows (once re-freshed)