Ryan, couldn't agree more, great article! These points are even more true for web apps.
To add to your first bullet point on "testing early", prototypes are also an excellent approach to getting user feedback early without spending too much time or resources upfront.
Prototypes can be created for example with paper in a matter of a few hours. When this is tested against real users, I have experienced numerous times how the data gathered from this study ends up saving dozens of hours of development time in the future.
Early in development, I have often experienced spending hours developing features that the target audience could care less about. Testing early definitely avoids unnecessary development. Your product turns out to be something users really utilize and care about from the get go.
Thanks Ryan! K

