I've found http://www.coda.cs.cmu.edu/ and http://code.google.com/p/tsumufs/
Both of them look as if they are trying to solve exactly this problem, but both look like interesting research projects not really ready for production use. Am I wrong? Have I missed something?
If I fall back on "have a local copy, sync regularly with the server", any recommendations?
("Make it all a DVCS repository" (bazaar looks a front runner, git another strong possibility), and Unison are possibilities.)
(And, related, I want to be able to login while disconnected, but keep account information in step with the stuff currently using NIS.
Use "ypcat passwd" (while connected) and compare with local entries?