Nice blog on what GeoCommons is doing to federate data: http://blog.fortiusone.com/2009/02/24/federating-with-geocommons-trying-to-keep-it-simple-and-standards-based/
Could be nice to do something along those lines, to work in conjunction with GeoCommons appliances. Not sure there’s a will for it, but something to keep in mind if anyone asks to be able to search across GeoServer instances. He doesn’t talk about it much, but I wonder if they do any smarter syncing of the data.