[foobar99]

What would happen? The customer would know beforehand what is true, anyway.

Berlin Brandenburg Airport was estimated to be opened in October 2011, then 2012, and currently 2013. Costs were estimated with 630 million. The current estimate is 1.2 billion.

Not giving an estimate isn't the entire solution, either.

The problem with an airport is that every time a deadline arrives, all you can do is notice that you don't have an airport, yet. You must estimate again (and you're wrong again).

With software you can say: "We're going to give you a shippable version every week. You can cancel the project at any time and you keep what you've paid for so far. We can screw up completely and you still have last week's shippable product."

Personally, I'd love that pay-as-you-go approach for the rest of the world.