I was notified this week that I accidentally left a timer on in my hours tracker. I received an email and everything. Harvest feels very in-tune with my schedule, and by using little more than a warning message and a notification, incorrect hours are resolved quickly and easily.
A great little read over at Invison about microinteractions. I find the psychology around these fascinating. Microinteractions need to remain invisible, yet provide the user instruction or feedback. It becomes such a subliminal thing.