In summary: They're a bad idea because they're extremely hard to get right. You'll almost certainly create a program that works at most 99% of the time, and yo

In summary: They're a bad idea because they're extremely hard to get right. You'll almost certainly create a program that works at most 99% of the time, and you'll never figure out what happened to the other 1% (my words, not Ousterhout's). He suggests events as a simpler alternative. I would add: Unless you use a language with convenient concurrency semantics like Clojure.