If you use Go's time.Sleep(), the goroutine will yield to all other goroutines while it is sleeping. Unfortunately, as georgemcbay says, using the system's sleep impedes Go's runtime as it cannot use that thread to run any goroutines in that time.

But yeah, I would say that is one of the quirks of Go at this time. You definitely need to be aware of how the scheduler works if you're using it in production.