Haven't logged into your Hotmail, Windows Live ID or Outlook in a year? Your user name might belong to someone else now.
PC World reports that Microsoft has confirmed to Webwereld, a Dutch publication, that the company reuses email account names from accounts which have been left dormant. Microsoft's Services Agreement states that users are required to log into their accounts "periodically, at a minimum of 270 days", and the company confirms that when the account becomes inactive it's "queued for deletion. Then, after a total of 360 days, the email account name is made available again."
Read more about Microsoft's policies, as well as Yahoo's and Google's, over at PC World. In the meantime, you might want to log into your email account.