Opinion or Legally Admissible?

Before starting my own business in 2004 I worked for a national optical chain. I held many roles over almost two decades and during the course of my employment I was named in a few law Suits; disgruntled employees, franchise owners, etc.
On one occasion, as my lawyer prepared me for deposition, he asked that I produce any written documentations: notes, journal, files, calendars, even birthday cards etc. Anything that had been written that could conceivably pertain to the case.
He commented to me that there were two schools of thought about documentation; either write EVERYTHING down or write NOTHING down.
Either way – at some point, it could be used to define your character, work ethic, or defend your case in a court of law.
Today with people sharing their thoughts and opinions on the Internet through blogs, MySpace, Face Book and the like – we are essentially doing the same thing; creating documentation that could be used for or against us sometime in the long distant future.
In reading Marketing Profs Daily Fix, I found a post that mirrored this feeling: "Don't Let Your Blog Come Back to Haunt You."
As an employer/manager/employee you should be trained not to write something down that you wouldn't want produced in a court of law.
Looks like the same can be said for what we write in our postings.