Quick show of hands: how many of you have computers around the house that are used by multiple people? Probably a lot, me included. Giving each user their own OS account is the easiest way to keep data and preferences separate on a single system, but that's probably overkill for shared PCs living in the kitchen or on the coffee table. For computers that spend most of their time running a web browser, the new profile manager built into Chrome 16 might be better option.
Each account has its own set of preferences, applications, and extensions, all of which rain down from the cloud. The only restriction I can find is that each Chrome window can only be associated with one account; you'll have to bust out multiple windows to use more than one profile. Oddly, switching profiles pops open a new window even if there's nothing loaded in the current one.
I have to admit that I've never been particularly big on customizing my browser with multiple extensions, applications, and other widgets. Being able to restrict those extras to a separate, easily accessible profile does make me more inclined to tinker with Chrome's look and feel, though.