I don't like to keg the Hefe, I think the flavor is a little better in the bottle and it loses that a lot quicker in the keg for some reason. Definitely drink them young though to get the best out of 'em.
Random tip: to avoid a crystal-weizen, I was told to store my hefe's upside down. Kind of hard with corny kegs, but try keeping the yeast in suspension.
Yeah sometimes commercial hefe kegs will come with instructions to store upside down so that when they're flipped over to kook them up, the yeast is put back in suspension. A simple shake will do the job too though...
It's not exactly a hefe but when I make my blue moon clone it seems to be at it's best after a week or 2 in the keg and i set it at 30psi for 36 hours and then down to about 12 or so to finish carbonating