Google has updated its webmaster rules on the use of links and keywords in press releases and it doesn't look good for PR agencies and their current suite of services. The details on the changes are here: Link schemes - Webmaster Tools Help
Any links intended to manipulate PageRank or a site's ranking in Google search results may be considered part of a link scheme and a violation of Google’s Webmaster Guidelines. This includes any behavior that manipulates links to your site or outgoing links from your site.