Search engine optimization is an ever growing and ever changing field, and as search engines and the Web change, so does SEO.
There are no classrooms, nor college courses, no single one site or conference series or book that can help you keep up with those changes.
Paying attention to a lot of blogs, news reports, press releases, and other sources of information can help provide some insights about changes in SEO, and discussions at forums and conferences and social sites can present a lot of signals and noise about what might be new in search. It’s not always easy, and not always even possible to distinquish between the signals and the noise sometimes.
I look at a lot of patent filings and papers from the search engines here because they can provide views of how search engines may work from the perspective of the search engines. I consider them primary sources because they come directly from the search engines, but even those sources often only provide glimpses of possibilities rather than actual insights into how search engines function.
Perhaps the best value that may be taken from search engine patent filings isn’t so much the processes that they describe, but rather the hints of assumptions behind some of the methods and systems that they present.