No, I am with BMMF on this; forum 'personas' are a myth. The only time I have found someone different in real life to how they are on here was when I discovered Balki was not a middle aged German woman. Other than that I think what people write on here is a very good guide to what they are like.
^This*
Specially the Balki one.
*I know you love 'this' posts ;P