A warning to PR agencies, Google is in the business of promotions and it doesn't like competitors! Google recently updated its webmaster guidelines: Watch your keywords and don't use them for manipulating your client's site's rank or your client's site will be penalized!

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 ranking of your site:

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."

Any attempt to promote your press release, with multiple postings to different sites, and other measures, other than its natural gain in popularity will raise a red flag at Google:

You must, "create unique, relevant content that can naturally gain popularity in the Internet community. "

 More on this topic here at SEOBook: Google: Press Release Links