Russel Buckley at the Mobile Technology Weblog has written "A Manifesto for Taking Wikipedia into the Physical World," an exploration of how the Wikipedia concept could be extended to physical spaces. He's essentially arguing for an open urban informatics model, one combining camera phone networks, virtual tags and location-based services. What makes his argument novel is that it makes the wiki concept central to the model -- anyone can annotate, update and edit.
The information would be from a variety of new and existing online sources. Some compiled especially for the Mobile Wikipedia by citizen contributors, some merely linked to sites that are already there. Citizen journalists would create the physical world links and then edit how the information was presented online - probably when they were back at a terminal more suited to the purpose. This might be a PC, or when they were able to dock their phone into a larger screen and keyboard combo.
Like the original Wikipedia, it would have potentially unlimited links and content and would be self-editing.
The argument isn't entirely new, but Buckley puts a nice spin on it, and explores some of the issues raised by trying to implement it.
H2G2 all over again. DNA was a visionary.