Letters is an abstraction layer over the ways many people detect problems with code in the real world. (I see these patterns re-emerge every day.) A debugger is part of the solution. Easy profiling and object diffing are another. Detecting how vulnerable you are to XSS attacks is yet another. When you have the power to do this inline without breaking your code apart, I think you gain productivity.

In other words, these patterns are not something we should have to spend brainpower on.

I probably should not have put the screencast on the front page -- it's actually about rationale and not about code examples. You can find concrete examples at http://lettersrb.com/api