Until recently, I was able to log into Stack Overflow using the webbrowser (Mobile IE) on my PS3. The latest PS3 update appears to have added better session support to the browser, so I don't know exactly when Stack Overflow stopped allowing me to login.
Currently, if I go to the login page I see: "or provide the openid:" - there's no images & links to forward to my provider for sync'ing authentication.
I had noticed a few weeks ago that functionality had been severely limited - no voting (up, down, on comments, or to close). All I could do was edit the question and add/edit answers. But adding answers was now prompting me with a captcha, though I was logged in :/
It was a pain that I'd get a 404 on successfully adding an answer, though refreshing would work just fine. The captcha addition didn't change anything with this regard...