XP is big on this. Not that I've ever managed it myself ... 8-)

http://www.extremeprogramming.org/rules.html

For me I guess it depends on the project, the timelines, the users, the requirements. Usually the users don't know what they want, so it is a constant iterative process of prototypes until they say "that's it!" and when you say you want to start again doing it properly it usually goes quiet ... and the prototype goes into production.