Dry hopping is great, BUT, keep a few things in mind. You have to drink the keg quickly (most of these will be IPA's, and you should drink them fresh anyway). The aroma will fade. Also, I learned recently that if you keep a beer in a keg with hops for too long (like over 6 months), tannins start to leach out of the hops. I have a partial keg of a Chinook IPA that I'll have to throw away because it'll make you pucker severely.