Google has updated its webmaster rules on links and keywords in press releases and it doesn't look good for PR agencies.
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.
If you repeat the use of a word in your press release, Google will think you are trying to stuff it with keywords and try to trick its index. Repeated words are a big red flag (I've put them in italics to explain what Google means by "optimized anchor text.")
Links with optimized anchor text in articles or press releases distributed on other sites. For example: "There are many wedding rings on the market. If you want to have a wedding, you will have to pick the best ring. You will also need to buy flowers and a wedding dress."
Most press releases are posted on numerous sites to get attention and to promote a business . This is now against the rules. Google doesn't want to see any unnatural boost to the popularity of a piece of content.