Good for the simplest of "rich" interactions, but quickly drops off when responsiveness becomes a factor. For example, you cannot implement optimistic responses using this library (click the "save todo" button and the saved item immediately appear in its read-only interface; this interaction requires reimplementing your templating library and validation code on the client and the server).
It isn't a perfect fit for every app, but most apps have at least a few areas where using it would simplify things considerably.
Also, there are a lot of nice things that are extremely easy to use that are a PITA with most other frameworks. For example, AJAX-aware history is an ic-push-url="true" away:
I realize that most front end people who see this will immediately dismiss it as "simple", but it's a very rich library and can be used to accomplish an awful lot: you can fire client side events using custom HTTP headers, show and hide request indicators using only a CSS selector, etc.
