Earlier quoted context omitted.
No, I don't think what google does is standard behavior (not trying to say anything bad about Google; I love Google). However, as far as I know, disallowing + is not a particularly good way of preventing abuse. I won't go as far as to say it semms like bad code but it is pretty close. I think it is OK to make a special case for Gmail and Google mail but it is counterproductive to try to crown it as a de facto standar…
huh? Google's special behaviour is that they are blind to dots in the user part of the address. The + sign is not anything to do with Google.
I just assumed + is a valid character and a+b@example.domain would be a valid email address independent of a or b. But it seems we shouldn't allow + or -- when people sign up for a new email address?