http://www.cisco.com/en/US/prod/collateral/routers/ps10538/data_sheet_c78_556319.html says: " A new, innovative, mini-B USB console port supports management connectivity when traditional serial ports are not available. The traditional console and auxiliary ports are also available. Either the USB-based console or the RJ-45-based console port can be used to configure the router."

Also, the unused space isn't always in the same place. The button is. Anyway, read the whole thread. It was fixed hours ago with an extension.