I am having the exact same issue, but running my shared media folder on a Mac Pro Lion Server. On that computer everything works fine. Neither our Lion iMac nor brand new MacBook Air see any books in the shared iTunes Media folder. They see and can access everything else. Books are a mix of epubs and pdfs. Prior to tonight's 10.4.1 update, the books list was at least visible on my older MacBook Pro running 10.6.8. Now that has stopped working. Installing 104.1 did nothing to fix books not showing up in the shared library on the Lion Macs.