If you are a PR writer and you don't know these rules already er, shame on you! Because when it comes to wrting for the web, the rules are completely different for print.
But trawling the net, you come across some huge howlers from even some of the big PR companies and newspapers as well.
What you have to bear in mind is that firstly many people are scanners - that polished 100 word copy on that great product won't attract many eyeballs if it's dense and full of marketese.
Kiss really does rule. I once took a class of PR students and it was an experience. Perhaps I shouldn't have asked them to buil websites !! £@%$
But the one area that should be a top priority on theire list, should be knowing how to write online for search engines and you the reader.
For a good read about this, and it's stood the test of timethe traditionalists can often the the best, go to Jakob Nielsen useit