And just perlmonks.org vs. www.perlmonks.org (or even testing.perlmonks.org) makes it somewhat difficult to have multiple login states since cookies get shared in one direction in such a case (but not in the other direction).

If you have "www." and "testing." no cookies will be shared between those two (if the cookie domain is not set to "perlmonks.org" explicitly, of course).