There's an interesting debate going on via the Code4Lib email list regarding the API. Specifically, should they have used SRU or is exposing a simple API better? Personally, I'm all for simple APIs that non-library techies can pick up and run with.
I've worked as a developer in libraries now for nearly 14 years and I've never used (or even seriously looked at) SRU. When I read the specification, I can feel my eyes begin to slowly glaze over! Perhaps this is just because I cut my teeth writing EDI processing software in COBOL and I've always suspected that people who develop specifications for use in libraries (e.g. Edifact, Z39.50, MARC, etc) are all a bunch of masochists