It varied for me. Sometimes daily or sometimes every few days. Normally at least after a few hours of watching something, but that varied to. However, since the update this problem has not happened again for me and I have been using Home Sharing for around 3 hours a day.
I've started having this issue in the last week. It either has to be with an apple tv or iTunes update as those are the only 2 changes I've had in that time. Also, if I airplay the same file from my MacBook, via quick time to the same Apple TV, no stuttering. So it's not the file itself. Its either iTunes or home sharing.