I signed the manifesto with the following motivation:
Agile Development represents to me agood way of thinking the development of a complex software. What I like the most is that changes are not scaring, but they are accepted as the development proceeds. Moreover, forcing small and frequent releases gives you and your client the feeling of having a product, even if still not complete. This is very important for the client, that can feel the development and can take control on it (meaning that she can collaborate with the developers in a "just-in-time" way), and it is very important for the developers too because they are forced to concentrate on incremental and significant changes, and they will not blow away a build.