There was a great post on TechCrunch about Yahoo embracing the semantic web. Basically, the semantic web is the ability to extract meaning from unstructured content. So if LinkedIn marked up their content with microformats, then others could quickly and easily leverage that data.
Michael Kimsal posted a response that caught my eye about why would LinkedIn want to make it easier for others to use their data, that it would allow freeloaders to take advantage of all the work LinkedIn has put into building up their network of data.
But, I think the key point is that the Semantic Web IS NOT meant to help closed networks like LinkedIn. The same way that HTML and the browser led to the downfall of AOLs walled garden of content, the semantic web means to break down the walled garden of data built up by companies like LinkedIn and the other social networking sites.
Im sure the prospect of people marking up their home pages with hResume microformatting tags, and listing their friends and acquaintances using XFN has the executives at LinkedIn shaking in their boots. Because when Yahoo indexes the web, and matches my XFN and hResume marked up data with similar information from all my friends and acquaintances (maybe via the homepage that I use for my OpenID profile???) then we no longer will need LinkedIn.
The Internet is the Social Network, and the Semantic Web provides the bones for that.