Does Stack Exchange own the content that I post?
What do I do if I want all of my posts and my user account deleted?
Under the terms of the CC license we (apparently!) grant on posts, you can't demand it be removed as the license is irrevocable, but you can ask for your attribution to be removed. The post is then no longer associated with your identity.
For more information, see the legal code of the license. The Stack Exchange sites are a "Collection", in that they are a collection of our individual CC-licensed works. Clause 4(a) has this to say regarding Collections:
"...If You create a Collection, upon notice from any Licensor You must, to the extent practicable, remove from the Collection any credit as required by Section 4(c), as requested"
You own the content you post here, but you've also agreed to release it under a Creative Commons license. You can see the logo and link at the bottom right of every page.
I am not a lawyer; I have too much common sense ;-)
Common sense says that if I ask a question and someone answers it, the collective thread is a collective work. But if I answer a question and then delete my answer, that is not a collective work, it is an individual contribution, which I have now revoked. If someone had commented on the answer before it was deleted, then it is a collective work.
We could argue these points in circles forever. Common sense says that if I delete something I posted, I don't want it to be seen any more.
It's not so much a matter of privacy as it is a matter of comfort. The delete button makes it okay to make mistakes. That comfort factor is now gone.
There could be a legit reason for this. Off the top of my head he could have been discussing some technologies or practices at his employer and they may have policies against that - especially if it is a DoD contractor, etc. his mistake in that case obviously.
There are of course other reasons. This may not be just someone who wants to take his ball and go home.
If there is a legit reason that Jeff or the other owners are suitably impressed by perhaps they will delete all your content from SO. You are SOL with external caches though unless you can get court orders...
SO is a community site, anything you post here is public, just like any other forum, blog that accepts comments, or any other website. The information that you post here, one way or another will continue to exist in most cases for a long time to come. You have to consider the Google Cache and other items as well, outside of SO that would have "copies" of your content.
If you don't want it displayed, don't post it...