Show how wait and notify solve the semaphore implementation problem. Mention that they can be used to implement any scheduling mechanism at all. Do the readers and writers problem with monitors. Java is making monitors much more popular and well known. Semaphores use a single structure for both exclusion and scheduling, monitors use different structures for each.
Monitors are more than just a synchronization mechansim.
Basing an operating system on them is an important decision about the structure of the entire system. I hope to talk about how operating systems are structured later in the course.