Forbes’ Ken Krogue writes a good article on the changes (demise?) of SEO in The Death Of SEO: The Rise of Social, PR, And Real Content. There are many important points in the article, and I highly recommend reading all of it, but the point I want to focus on is this:
The bottom line is that all SEO efforts are counterfeit other than one: Writing, designing, recording, or videoing real and relevant content that benefits those who search.
Recently, I’ve been spending time discussing the “ethics” of various discoverability options, and it generally comes down to: you can do it until Google says you can’t. Which is really not a very satisfying rule.
That’s because Google’s rules are an attempt to get at criteria that weeds out crappy content — sites that are misleading or fraudulent, or even just plain weak. And, though it is fun to pick on the leader of the pack, Google doesn’t weed out crappy content on a whim. They do it because their users want quality content. (Admittedly, Google’s throws out a bunch of providers of quality content with the bathwater.)
But the key is quality content. If you have quality content as the foundation of your site, SEO, SEM, social media promo, et al, are just tools. 
And that’s the Catch-22. In our attempt to develop content that can pass the muster of Panda and Penguin and the entire zoo of Google’s (not to mention other search engine providers), we risk stripping it of meaning. Search Engine Watch has a good summary of effective SEO. The basics are captured in this hierarchy of needs approach to SEO. (Maslow certainly has long legs.)
But as the foundation of the hierarchy (and I’m sure SEW would agree) is quality content.
Great content makes the marketing easy. If you are struggling with SEO, look first at whether you have unique, rich, usable content. Take the time to develop a comprehensive and compelling content strategy. (Got to love alliteration.)
Then make it easy to discover.