You may remember that a while back we launched remote sign out and information about recent account activity to help you understand and manage your account usage. This information is still at the bottom of your inbox. Now, if it looks like something unusual is going on with your account, we’ll also alert you by posting a warning message saying, “Warning: We believe your account was last accessed from…” along with the geographic region that we can best associate with the access.
This is awesome, but I guess it means that I’ll have to stop stalking all my ex’s gmail accounts, boo. via Official Gmail Blog: Detecting suspicious account activity.