A very small chunk, I only lasted a couple months. Most of it was pretty boring, think volume after volume of copyright records or issues of the national stamp collector's magazine. Eventually I started working on some of the contract work they did for other agencies, e.g. declassified FBI case reports. The best was the stuff for the Smithsonian, which often included beautiful naturalist illustrations. I'm not sure how much of that stuff was public domain though.
When scanning books like that did you ever see anything interesting or are you so zoned out you don't really pay attention?