Maybe a separate % complete or similar, with a slider, so I can figure out that I'm halfway done a task that is supposed to take 3 hours but I'm 90% done a task that's supposed to take 10, so the 3 hour task will actually take more time.
I really like the idea of a stopwatch function. I.e. I'm starting this now, hit go. When finished, hit "stop" and the time gets logged. I've seen that on another to do app, but I can't remember which one.