Gmail has introduced a new privacy feature that will let users see how many computers their account is open on, and also allows them to sign-out remotely. Basic information is displayed as part of the page?s standard footer, and users looking for more detailed information can view a log that displays the most recent IP addresses to access the account, along with the type of access (Mobile, POP, etc.)
http://www.techcrunch.com/2008/07/07/google-gmail-account/