I accept that things haven't improved for a number of users, but the 4.1 software update has fixed the "stutter when the buffer has filled" problem described by many users for me.
I found this affected both rented movies and video streamed from my MacBook and it's gone as far as I can tell (once you've spotted it you become pretty well tuned into it). I am still getting a 720p/60Hz picture according to my TV.
The other issue I experienced that seems to have been fixed related to PAL material, either from DV or DVD, having terrible motion judder, most noticeable on panning shots. I initially put this down to the ATV's apparent inability to display anything other than 60Hz. However, previously unwatchable videos now display smoothly, even though the ATV still outputs a 720p/60Hz picture.
So i'm not disputing that many people still have problems or have new problems following this update, but it's helped me.
<Edited by Host>