It seems a tactic black hat SEOs are using to bring down their competitors is putting personal information on their competitor’s site and then reporting it to Google…
http://searchenginewatch.com/3641581
What’s interesting is that if you look at what information Google will take action on…
http://www.google.com/support/webmasters/bin/answer.py?answer=164133
While things like social security numbers, bank account or credit card numbers and images of a person’s signature are always a bad idea, for certain types of porn sites it gets tougher - they can’t have business names or people’s full names. It’s not just any porn site that gets the extra scutiny, but “low quality” porn sites. Low quality encompasses things like sites with duplicate content (e.g. sites that are fed by RSS feeds), sites where pages are loaded with irrelevant keywords, sites with hidden text, sneaky redirects, etc.
Now mind you, your low quality site probably isn’t doing very well in Google to start with, but if you have an otherwise high quality site with one section that’s low quality a competitor could post a comment with personal information and get Google to review your site and they could discover the low quality section of your site and suddenly the whole site gets deindexed because of the personal information.
Even those of you who think you’re running a clean ship - you could get penalized if you link to a site that gets banned/deindexed. I know a lot of you do link exchanges like crazy, but linking to low quality sites can hurt you
Curiously phone numbers and addresses don’t seem to be personal information that’s of concern to Google - probably because of sites like switchboard.com. But you still should be careful with personal information - especially if you do splogs.