My experience as well. I tried it a couple of times more than 10 years ago, one is covering Nancy Lynch's Distributed Algorithms, and one is Maurice Herlihy's The Art of Multiprocessor Programming. We finished about 1/4 of each of the books before running out of momentum. People simply lost interest as the content became increasingly challenging. We talked about the reasons, and the overwhelming feedback was that people lost interest because they failed to see what they learned could be applied to the job in short term, so it looked to them that the effort of learning the hard stuff wouldn't pay off.