Came across this recently whilst browsing one of those magazines.
What would you need this for?
Well, if I have my Google Mail Contacts open and I want to write a message to one of my contacts, but I also still want to keep … Contacts open – you never know, how long it takes to complete a message, but you still want to be able to look up contact details – then at least I need it.
On OS X you drag the tab to another place with the mouse or whatever and the Alt key pressed. On Linux and Windows it’s the Control key instead.