Once upon a time SEO meant stuffing many keywords in a page, repeating them to the exasperation of the users, eventually hiding them by typing them in the same colour as the background.
The technique is considered since years black hat, and no, it doesn’t work anymore, but you will still find such pages on the Web.
Then SEO was a bout the meta tags and stuffing them with keywords. This worked pretty fast and in some situations it still does, but most of the meta tags don’t have the same power anymore.
They title tag remains the most powerful meta tag, but that’s it. Links have always been important for the search engines, particularly for Google that used to base most of the SERP rankings on links. All the SEO techniques of the past are slowly becoming if not black hat, grey hat techniques.
What you have to understand is that, although keywords are still important, SEO has changed and keywords alone are no longer enough. Now the value of a site lays in the value of its authority. The authority is given by the number of links, traffic (particularly returning visitors, so forget about fooling the search engines by joining traffic exchange programs) and certainly content.
The content is no longer reduced to text only. You can enhance the value of your pages by adding pictures, video and sound and tagging them properly. Interactive tools give your site a plus of web appeal.
In my opinion the current evolution of SEO is clear: SEO is aimed at the humans and their likes and dislikes. And even the traditional search engines will follow the human users and will, eventually, all go social. It’s just a matter of how and when.