Yep, I just converted to nginx and the undefined index was driving me CRAZY in the log. After researching (and I'm not a coder by far) I stumbled upon the if(ifset code and once I put it into place ALL errors stopped. My log had gone to 256MB in just a matter of a short time before the code change.
I'm of the opinion that the changes outlined in this resource were never necessary. However, parts of the Facebook SDK that XF uses were updated in 1.4 so it's safe to assume that everything is as up to date as it should be.