Mozilla and Opera are working together to come up with a list of effective top level domains since it is impossible to determine where the registry controlled part ends.
Currently it is in the planning stages, but once implemented this would be valuable for creating pseudowords from domains in message headers.
Quoted from Gervase Markham's blog:
'For example, in "fred.com", "com" is the responsibility of the registry, and "fred" is the responsibility of the registrant. However, in "fred.valer.hedmark.no", "valer.hedmark.no" is the registry's part.'
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The list is now public.
http://publicsuffix.org/