After clicking on the "change" link, Google informs that this is an advanced feature and that it will only work for Gmail, Google Calendar, Google Sites, Google Reader, Google Voice, App Engine and Google Code. When multiple sign-in is enabled, a drop-down is displayed next to your email address at the top of the page, so you can quickly switch to a new account.
Explore large structures and what it takes to build them with BUILDING BIG™, a five-part PBS television series and Web site from WGBH Boston. Here are the main features of the site:
Bridges, Domes, Skyscrapers, Dams, and Tunnels.