I've been working on a project for the past couple months that involves using XMPP for client-to-client communication. While there are some good how-tos and libraries, the process would be infinitely easier if XMPP.org's documentation was in terms of reference examples and sample packets/messages, rather than incredibly dense specs written in convoluted techspec language that takes some time to comprehend, even when reading intently.
A refreshing counterexample is the RubySpec project. While Ruby began with only a reference implementation, the process of developing a comprehensive test suite that is able to measure conformance to the reference implementation has created an invaluable metric for other implementers.
While JavaScript has a very thorough specification, Sputnik's project of building a test suite that measures the conformance of an interpreter to the spec will be helpful in understanding how far we have to go, and in which direction we're moving.