+1 to numbering the incognito sessions. Sometimes I need to simulate two user accounts polling some web service, or perhaps simulate a chat-like environment. Point is: I need two separate cookie jars. I've accomplished this using profiles, or by using my incognito window for "user A" and a profile window for "user B." However, there's less overhead with incognito windows and for development scenarios (which are inherently ad-hoc and temporary), overhead sometimes makes all the difference.