We are almost certainly going with this for a boy. DS1 was nearly called it, but we chose something else in the end, because dh and I pronounce Francis differently. However he would always be Frankie at home anyway, so it's not really a problem.
The Pope thing is a slight concern for me, but he will not be going to a Catholic school, so I think it will be ok.
Also the baby's only surviving great grandparent is called Francis, and he's a smashing bloke :)