I can speak from my own knowledge on this, so as not to rely to heavily on 'Mr xara' (we love that by the way)

The cookies are used on this site quite a bit. First of all, they keep up with your login id and password. Otherwise the site wouldn't be able to know anything you did. eg. who makes which posts, the who is online bit, etc.. also, the website keeps up with which posts you have read. The problem with the cookies is just that. It makes a cookie when you open your browser or go to the site for the first time since you last opened your browser. Every time you read a post it takes the little NEW label off. It makes a list in the cookies of the ones you have read. So this list gets longer and longer as you go along. When you exit the site (I don't quite understand this, but mostly) it just remembers what time you were last there and which boards you looked at (q&a, miscellaney) so it only has to remember a time for each one, not each individual post. However, the cookie only resets when you close your browser. If you, like me, never close your browser unless something crashes, the list of numbers gets VERY long until it just can't cope anymore. Does that clarify?