This dumb mistake just cost me an hour spelunking around in the debugger:

var status = source.Substring(source.LastIndexOf("/" + 1));  

(where source is e.g. "http://foo.com/status/all-is-good")

Fortunately the ramifications were picked up in the acceptance tests, but the root cause wasn't at all obvious from such a high level.

Lesson for the day - code is never too trivial to warrant unit testing.