What are the most useful and useless metrics to track in SEO?

Question

For example, PageRank (or not)... :-) ...question, still stands, just no example now.

Factors include how actionable it is, consistency of availability, or correlation to ranking.

Answer 1

USEFUL:

Incoming link quality, links from high trustrank and pagerank pages with relevant content and keyword in anchor text. sans nofollow.

Unique non duplicate content, especially unique title and description meta tags. And sane keyword density in text, so text is not considered spam.

USELESS:

Position in SEM results, a myth many believe in us that appearing on AdWords affects your ranking.

Answer 2

USEFUL: Keyword Rank

Answer 3

Useless: Alexa Page Rank