I only say that in that I considered it, and decided on an external system directly attached to my Mac. Why?
1. You need iTunes running on a machine, and the machine running.
2. Data transfer over a network, (and mine is all hard wired CAT5) is slow!
(synced an ATV1 a couple of times...bloody painful)
3. Following from point 2, I have a 4Tb plus library for access by 5 ATVs. Backing that up over a network? Kill me now!
4. Generally ripping and such and then waiting for every movie to copy over?? Again, take a spoon and dig out my heart....it'll be less painful!
Currently with a Drobo attached via FW800. Its now to slow for my liking, especially since thunderbolt is here and available. Will soon upgrade it to a thunderbolt solution.
One point i must make...I dont jailbreak. Apple TV, iPhone, whatever. Tried it a couple of times, hated the fact every time a software update happened, the JB was broken. But a direct attached storage to an ATV (as long as its only one) would probably be a very tempting option to me.