"Things like mozRank and mozTrust have seemed to work out fairly well so far, but our testers and members have struggled a bit more with mozRank vs. Domain mozRank--one is for a page while the other applies to a domain--and been seriously confused about FQDs vs. PLDs," Fishkin writes. He describes four kinds of Web structures, and suggests it's time for a change if "the savviest of SEOs struggle to understand/interpret/apply this information."