[whpalmer4]

All of those are good points with which I agree, but I reach a different conclusion :-)

I only put estimates on things where I am very confident of the duration, or where the estimate will be particularly helpful. The most usual case of that is something that I know will be particularly short or long. I have a perspective called Quick Dash that will show me all of the available tasks which have an estimate of 5 minutes or less. This is useful for quickly finding something to do when I only have a little bit of time, or for finding a handful of things I can do to build up some momentum, if you will — getting a handful of things done will get me rolling, whereas tackling one big thing when I'm feeling unmotivated often doesn't end well. Similarly, a search for items taking more than 1 hour can be handy if I have some uninterrupted time, plenty of energy, and want to tackle some of the tasks that otherwise never seem to get done.

In the end, only about 5% of my available tasks have estimates, but many of them are repeating tasks, so those estimates are pretty good and well-amortized. In general, I don't make much overall use of the duration estimates because of the problems pointed out by wilsonng, but there are some areas where value can be had even though most tasks don't have estimates.