Jonathan Rees pointed me to his document Common Naming, a "memo about effective use of shared URI's to link semantic web projects." It outlines a vision scarily like bioGUIDs, but with the added use of Persistent URLs (PURLs). To quote from the introduction:
In order for independently developed semantic web projects to work together, they need to share names for things that they both talk about. Common choice and consistent use of URI's forms the backbone of the semantic web.
For example, if two resources or applications talk about a database record (or the things it describes), they need to use a common URI for the record if a combination ('mashup') of the two resources is to connect information that each resource has relating to that record.
This is not generally the case now.
I see this document as reinforcement of my feeling that the lack of good URIs is perhaps the main thing holding us back from building really cool applications.