Any user can edit their own posts on the MSDN Forums with the graphical “Edit” button.  Moderators have the ability to edit any users post by clicking the “edit post” link in the upper right of the post.  When you edit a post you are required to leave notes that include “edited by [user name]” that will be visible to anyone that reads the forum about the change you made. 

Reasons for editing a post would include, but are not limited to:

• Minor inappropriate language - Removal of inappropriate language that was not caught by the site language filters in an otherwise appropriate comment. Remember that these posts go straight into Visual Studio's help search!
• Typos - If you happen to catch an obvious typo in an otherwise good post that you think would cause unnecessary confusion for readers of or searchers for this post
• Search Enablement - It is a very good idea to correct errors in Namespaces or class names to that that later users might enter these as search terms and have it retrieve the post correctly.
• Bad Information: If the content of a reply or post is mis-leading or contains information that is wrong for the end user to follow a moderator should edit the post to ensure users who find the post don't get misleading advice.  If the wrong information is tagged as an answer you should consider posting a new reply with good information and moving the answer tag to the new post with better information. 
• Misattribution - If a user creates a post that is obviously a comment when it should have been a question or vice-versa.  The most common case here is when comments are incorrectly entered as "questions". A comment might be "Hey, look at this cool new article on foo" that does not require an answer.  If this was tagged as a question you should go back and change it to an attribution of type = "comment".