Another mention of SRU: the discovery+ project at Edinburgh has brought up an SRU demonstrator.
SRU is a web services protocol for federated and parallel (e.g. via merged/union catalogues) searching of multiple bibliographic repositories. The protocol is a REST type protocol in which search queries can be requested via HTTP calls with results returnable in various XML schemas. The d+ project is piloting web services (this demonstrator) and toolkit capable of searching library and resource gateways and transforming heterogeneous search results to reusable and standardised schemas for e-learning purposes. The search output from this demonstrator is based on the SRU result wrapper with the IEEE Learning Object Metadata (LOM) binding. Mapping to other schemas including IMS Content Packaging and Resource Lists Specifications is in development. [Discovery+: Brokerage for Deep an Distributed e-Learning Resources Discovery]
The project also runs a test Dspace repository which hosts collections searchable under SRU.