damn you've cracked the code for this weeks lotto
mine says 3 at the moment, it should be calculating the amount of posts that have been made that you haven't read.
now the way it works out if youve read/seen or not could be alot of different ways.
if you click the new post button/link it should take you to the 3 posts (in my case) that i havent read since my last visit.
other than that ive not no clue, but will take a closer eye at it from now on.