I just threw together a pillow using a standard piece of copy paper as a pattern (8.5 x 11"), and 1.5 oz of 800 fill down. Here is the results:
This is a 750mL Nalgene - about the same height as a regular quart size.
(I really need to get a better camera...)
I think a back sleeper could use it fine, but as a side sleeper, I'd want more height. It would be fine if you had something about 4" high to put it on, but otherwise, more down would be needed.
- Ben Smith