A simple test suggests otherwise, using Gruez's recipe above but swapping the private and non-private windows. There are potential information leaks, such as t

A simple test suggests otherwise, using Gruez's recipe above but swapping the private and non-private windows. There are potential information leaks, such as the combination of IP address, user agent, screen size, and fonts available. And there may be bugs in 3rd party plugins like Flash that fail to respect private mode. But it doesn't seem to be anything as simple as cookies being shared.