If given the choice to target users based on GMail data or targeting users based on Facebook data, I would take the former. GMail data would provide you with a

If given the choice to target users based on GMail data or targeting users based on Facebook data, I would take the former. GMail data would provide you with a much clearer and nuanced profile of someone, even if GMail has only 1/3 - 1/2 the user base. Facebook should do well with consumer brands though.