The recent workshop on Open Data on the Web sparked some reflection on the geospatial field's ability (or lack thereof) to deliver options for "ultra-lightweight" data publishing formats. The observation that stood out most was that most people still want to publish tables -- tabular data! XML and RDF will never appeal to a large cross-section of the IT world.
There are several Open Source, Free-Ware, and Commercial Off-the-Shelf (COTS) activities committed to the development of Sensor Web Enablement (SWE) oriented software. This includes software to support servers, middleware, and clients, as well as tools for creating and validating SWE encodings.