ungetable http URIs

We were playing with some simile data in haystack today and discussed
briefly the fact that simile is defining URIs in namespace
http://www.mit.edu/simile/ that are not http-GETtable---ie, they return 404
not founds.  Apparently there has been some discussion of this
approach but I don't think I've weighed in.  If we don't ever plan for
the URIs to be http-GETtable, there's no reason for us to use http
URIs: we could do urn://www.mit.edu/simile....  This would avoid
browsers getting confused.  Alternatively (and this is the approach
I'd like to  see) it would be nice if we had a web server that
returned some useful RDF when we tried to resolve such URIs---just in
case the requestor was able to cope with that (as haystack can)

-David