My apologies to the anonymous visitor whose off-topic comment I initially rejected. Let me answer your question.
By social media, let me define it by example to be services like Google Wave, Facebook, Orkut, Linkedin, Twitter, Digg, Reddit, Slashdot, and others. Let me consider blogs separately from these.
By SEO, we mean Search Engine Optimization, or the art and science (yes, both) of crafting ones content and metadata in a search-engine friendly way so that one's website is most accurately represented (not misrepresented) and, thus, can be found by those likely visitors who, in the absence of good SEO, would not have found the site.
SEO works brilliantly on static websites (those composed of .html pages, which are updated "manually" or with the help of half-way automated tools). The content is prepared, so it is easy to provide SEO for that content at the time of preparation. For dynamic content, on the other hand, while it is not difficult to provide SEO at the time of the content's creation, it is unpredictable how to access the content (a permanent link) or it is the mere dynamic nature that can result in omissions of content (content was posted and then changed before it could be indexed), or the information on the site is dependent, somehow, upon various characteristics of the viewer, especially geography - search engines must be able to pose as each combination of characteristics the site responds to and thereby make a complete index of the content.
To this end, search engines have now adopted the Sitemap idea, which provides (possibly dynamically) a list of the pages on a site, along with how frequently they are updated, in an easy-to-parse and flexible XML format (see http://www.sitemaps.org/). This helps search engines to find the pages that are generated dynamically, and to which there may not be obvious links elsewhere on the site.
Social media (let's take Twitter, for example) can only kill SEO if it is the only place that content is created on the web. This is because it would be exclusively within the control of the social media service to index and provide searchability of its collective content (within appropriate access permissions). Twitter and Facebook news feeds are "live," meaning that as soon as matching or "relevant" content is available within the system, it will be added to your feed, as you watch. This is a nightmare for public search engines, but within a corporation, especially with a cloud-based functional engine driving it (like MapReduce), queries can be performed on practically up-to-the-second fresh content. In this regard, SEO would not be needed.
So it seems that the art and science of optimizing the content available on a website in order to ensure that search engines out there can detect and index that content for the public to search is far from endangered, but rather will remain in demand for quite some time. SEO, as a business or professional service will certainly continue to change its practice to accommodate new technology and maintain its place in the midst of the automated tools that support it, but SEO is most certainly not going to be killed by social media.
Registered Linux User #370740 (http://counter.li.org)