I'm not a Search Engine Optimization expert. I enjoy thinking about it, and I have a pretty good idea about SEO best practices but I'm not a pro.
The real SEO pros who live and breathe the stuff all day, every day.
I'm talking about guys like Rand Fishkin at SEOMoz because he writes amazing posts like a recent one about How To Build A Perfectly Optimized Landing Page.
In that post, he walks through his thoughts on how a page should be built in order for it to have the best chance of ranking well in search results. I won't repeat it all here, but he provides well-researched data for some of the reasons he gives, and explains it all in easy-to-understand terms.
Near the end of the post, he asks the question "Why don't we always obey the rules (when it comes to optimizing landing pages)?"
The gist of his answer is that the reasons SEO pros don't always ignore these landing-page optimization rules is because they are focused on other strategies, such as link buidling, to achieve search engine dominance.
Although he lists both Content and User Experience as other priorities one should have when building a landing page, I don't think he ranks them highly enough. To me, it seems like having good content and ensuring that is easy for your users to navigate should take precedence over any other work.
Its fine to rank well in search engines, but that's not going to do anything for you if users aren't interested in what they find on your page, or if they have trouble doing anything with it.
As always, plan and create for users first, search engines second.