This was actually supposed to be in response to a different post, but since that post was in the apple tv forum and I'm on os x, I thought I'd post here and then link back.
I'm having problems with smb streaming (as others seem to have). It starts off fine but then becomes very "laggy". This is with all of the caches set to their maximums in guisettings.xml.
The videos are on a NAS with upnp, smb, and ftp servers, and none of the folders are being indexed as I have them set to private to avoid this.
SMB streaming seems to start out fine (I can see it pulling down 1.2mb/s), but it quickly slows down and the video and audio become choppy. UPNP behaves similarly, although it never reaches 1.2mb/s. These same videos stream fine when the smb share is mounted in os x (thru QuickLook, vlc, whatever...). They also stream fine to my iPhone using upnp (with PlugPlayer). Given that they stream fine in these other situations, it seems odd to say that it's my connection's fault (wireless g).
I'm currently using ftp. It is working better, but the videos still stop to load or buffer throughout the episode.
Let me know if some logs would be of help with this. Increasing the size of the cache seemed to me to be the best bet, but it hasn't helped. I'd be happy to hear of any other suggestions.