Lately I've been running into a lot of questions regarding the current changes with Google search engines and how sites are ranked. The question came up, are SEO companies legitimate anymore? The answer is yes as long as they are following white hat techniques outlined by Google.
Search engines still need to be able to understand what your web pages are about. We optimize those pages with well known techniques for page titles, content markup, filenames, ..etc. What we don't do is use keywords too many times (keyword stuffing) or over-optimize the content. (Spammy) The rule is if it doesn't sound natural you run the risk of being flagged for spammy content.
Matt Cutts at Google explains:
The real point is you don't really want to try to manipulate search engines or you run the risk of being penalized in the future. What you should be doing is creating search engine friendly content and backlinks to build credibility with your website.
So yes, you do need and SEO professional to optimize your website and the good news is it's just getting harder to do bad SEO which is good for everyone.