ADL have released a report on the various technologies currently being employed to create repositories of learning objects (or data elements depending upon your terminology). The report is detailed and technical and naturally takes a SCORM-centred view but gives a fair introduction the current state of the art. Cutting to the chase, the risk assessment at the end suggest that lack of standards, vendor uncertainty over which technology to use, the lack of a sizable developer community and competing unique identifier systems are not helping. So no surprises there.
The repository projects reviewed are: