Eighty percent (or less)

The people who work with me get really tired of proposals that we build initial versions of our tools with as few features as possible. My default position is that it is better to ship something that doesn't have all the desired features than to ship a more full featured something later. Or worse, ship nothing at all.

Here's the deal. There is always a reason not to release your product. The worst is the mythical missing features. These are the features that will cause your customers to refuse to use the tool. They can't live without it. They won't use it. You'll be wasting your time releasing it.

Take the new off-line features of Google Reader for example. I looked forward to using it while traveling, but was sure it would be deficient because I knew I wouldn't be able to chase links or see embedded images within the Reader. I gave it a try anyway, and found the ability to plow through several hundred items while at 38,000 feet to be extremely useful.

Prioritize your features carefully. Implement them well. Shut up and ship.