Agile Development: Warning Signs
Alok Srivastava has an excellent post discussing agile development and areas that can put agile projects at risk. I'm currently doing clean up on an agile project gone south, and I wholeheartedly agree that the issues he points out should be warning signs if you are considering agile development. That's not to say that agile is bad by any means, just that you should think carefully before you make the jump, especially if your project will have the issues Alok mentions:
http://blogs.msdn.com/isv/archive/2008/07/29/agile-methodology-and-new-product-development-four-key-issues.aspx