http://marekblotny.com/2010/08/estimates-versus-commitment/

If you are a member of development team, sooner or later someone will ask you to estimate something. It can be something small like a bug or task but it can be also something bigger like entire project. Regardless what that is, try to figure out what kind of answer you are expected to give. I don’t mean here that you should be trying to give the “right” estimate. I’m thinking about something different — usually there are two possible types of answers...