Should PR Pros Leave Comments on Client Stories?

The Tech PR Gems blog ran an interesting post earlier this week that discusses the practice of PR folks commenting on their own clients' stories. As the author notes, it's a fuzzy area that makes a lot of folks nervous:
"In talking about engaging bloggers in PR, we are often cautioned about astroturfing, i.e. posting while pretending to be someone else such as a happy customer fighting off criticisms of your client.
But what about posting -- as the PR person? It seems to go against the idea of the PR person being in the background and the official client spokesperson doing all the official client spokespersoning. So, I have often been reluctant to do so, preferring to identify conversations where the client should jump in on their own."
The post includes some helpful ground rules for those that do comment on their own stories.