Agile Methodologies are adaptive, iterative and incremental. Their effectiveness is well recognized in the industry. However, there is no silver bullet. The Agile Methodologies have their limitations and demand a close interaction among end users, business analysts, developers and testers in short cycles. It implies a break down of walls among divisions and the formation of a coherent and collaborative team from different groups. The Agile Methodologies work best for co-located teams. In certain circumstances this is simply too expensive or politically impossible. Another consideration point is the team size. When the size of the development team increases, it's agility decreases.
In a conclusion, think twice before adopting Agile Methodologies for large scale projects or distributed development teams.