Do I have to wake up a Power Nap enabled Mac to stream media off of it or can I leave it sleeping?
This seems to work on my AppleTV 2 and MacBook Air.
Last night I turned on the AppleTV to browse my main library on a Mac Mini and the MacBook Air library showed up as well, even though the lid was closed and the computer was asleep.
I have not experimented enough to know if this works with the power adapter unplugged.
This was a very pleasant, but apparently undocumented, feature to discover. Perhaps it arrived in the most recent AppleTV update.