WSDL is useful in the enterprise space where toolsets do most of the heavy lifting, but it really is too much hard work to write WSDL from scratch. Tim Bray muses about how WSDL could be improved, likening it to SGML for complexity and asking what the XML simplification would be.
Update: Dion Hinchcliffe has provided a good summary of the various alternatives that are in the wings at the moment.
There is a lot happening in this space, even if it is getting confusing. I’ve just been to a seminar where “AJAX” was quoted as the new web service. Amusing given how it is just the result of gluing together existing technologies in an interesting way.