an emoticon, most often used to highlight the somewhat funny, but more likely weird, odd or "dorky" nature of a comment. it is intended to look like a person in glasses (hence the "dorkiness") sticking out her/his tongue. often used in a self-deprecating manner after what is considered by the author to be a bad joke, or as an acknowledgment of the perceived lameness of the preceding comment.
related to :P
, and XP
. see especially Viscerae's Mar 16, 2007 definition of ;P
on Urban Dictionary.com.
of course, if you have been there, then just ignore this advice, and you can tell me to keep my 0s and 1s to myself. 8P