I think common sense is needed here. I think most of us make the odd typo, that's acceptable, but when a post is riddled with them it annoys me that the contributor hasn't take time to do their own spell check before they hit the 'submit' button.
I must admit I don't like to see people using 'of' when they mean 'have', also not knowing the difference between 'to and 'too'.
Having said that I wouldn't ban anybody from Answerbank, it could possibly be that English is their second language.