We had a good time at mashup. For me the highlight was a pow-wow of WSFinder, Programmable Web, and StrikeIron trying to figure out how to replace UDDI/WSDL with something simple and easy.
We kept saying, "lets keep this at the Yahoo directory level of complexity". Our proposal is a really simple "API RSS" that has 5 or 6 fields in it. This is about discovery and brief description, not implementation etc. This is just so a developer knows how and where to look for a list of APIs to mashup.
Check out this from Chris Law, the other half of WSFinder.