I posted this on another forum yesterday:
I only dryhop in the keg. I use hop socks with marbles (boiled first), fill them with hops, then toss them in and leave until the keg is empty.
One thing I have learned about dryhopping is that it must be done at room temperature (say 18C) for a period of time. If you dry hop at serving temps, you only get a very grassy unpleasant character. I add my dryhops, leave at room temp for 5-7 days, then move to the kegerator.
Many also have concerns about leaving hops in the keg for an extended period. I have discovered that this works incredibly well at maintaining a fresh hop character, but it is critical that you keep the keg cold after the initial 5-7 days at room temp. If you don't, you will get a harsh astringent hop character.
I only use citrusy "american" leaf hops that have been kept in excellent condition for dry hopping. Pellet hops have not yielded as good as a result for me.
I have played around with this extensively over the last couple years, and these observations and results have been very consistent.
When I am not experimenting and instead following my best practices, I have found it almost impossible to add too many dry hops - they impart zero bitterness/harshness, just massive amounts of juicy, citrus, dank character that does not fade away at anywhere close to same rate as similar commercial products (even when using relatively small amounts such as 1-2oz).