I would say that 99% of the ids made for yahoo! are used mainly on messenger. But when u go through the member directory, only 10% or so show them as having messenger. Never really messed with it much to figure out why it was like that, could possibly only show on ids that have been recently active. If someone finds you in a member search and they want to send you a message, they can do it on messenger. Not really that big of a deal, doubt most people ever noticed this.