The biggest problem nowadays, though, is that we're building sites more and more that aren't crawlable by the search engines. Basic site structure and usability

The biggest problem nowadays, though, is that we're building sites more and more that aren't crawlable by the search engines. Basic site structure and usability issues plague many sites. A good SEO will fix those issues. It's not the link building or content that needs to be fixed, what is needed is the skills of a competent technical SEO who understands web dev. In many cases a site just needs to fix it's site structure and the crawling issues and it will rank well. For example, I've seen plenty of sites that have over 1 million pages of content but the only way to get to those pages is through an XML sitemap--that's not SEO.