Windows: Google's Chrome browser doesn't have nearly the same kind of user profile control that Firefox offers. Until it's baked in, we have ChromeDeck, a handy utility that creates, manages and produces shortcuts to multiple Chrome user profiles.
Why maintain multiple Chrome profiles? Maybe you don't want the hassle of creating different user accounts for occasional users, or use Chrome for sometimes entirely different purposes — work and home — that you'd have different extensions loaded for. Fire up ChromeDeck, create a new account and shortcuts for it on the desktop, and soldier on with two distinct Chrome personalities.
ChromeDeck is a free download, requires Windows and the .NET 4 framework. Thanks for the tip, ArpitNext!