Appropriately, the first question that came to mind was, "what's the catch?" :)
I'm currently toying with writing a JSONReporter so we can use that as an additional test result output format and I agree, so far it seems to be a really well done project.
That said, inline setup/teardown and parsing expressions in asserts seem like such natural ideas, I can't believe I haven't run across frameworks doing them before. I guess the shadow of JUnit is extremely long.