I have been trying to come up with a layers of Web 2.0 diagram (a bit like the old OSI 7 layer diagram) which ties together all the buzz technologies and came up with this:   

  

Mashups  

Application

 Conceptual
Composite apps
Collaboration Edge
Communication
Discovery and Location
Search
Relationships and trust
Identity
Dynamic Languages Developer Logical
Compiled Languages
APIs / SDK's
WS-* Services
WS-Basic
A9
Atom
RSS
REST
SaaS Service Physical
Server Server
Devices Client