I love Things.app. I found many of the same observations about Omni Focus, and ended up switching everything over- Things is that good.

I, too, was initially confused about the use of "Areas" in things, but I got some clarification from the wonderfully responsive staff at Cultured Code. Areas can contain both single tasks and projects, thus they are an additional level of hierarchical organization to help you separate, for example, work and home, or several hats that you must wear at once.

Tags are non-hierarchical and can be very flexible, but Things.app reasons that you could get too many at once, so Areas takes some of the heat off your tagging system.

One shortcoming of Areas currently (1/28) is that the easiest ways to assign them require you to drag a mouse to drop things or to move around in dialog boxes. Additionally, you can't assign a task to more than one area (eg. I have buy life insurance under both "money" and "family" areas.) Currently, you can't filter things by area in the different focuses (today, next, etc), but they are sorted by area. You also can't collapse the Area headings.

I have found that I can use the Areas concept just by assigning a hierarchy of Tags for each area (Areas/home:work:etc), and all these problems go away. The hierarchical tags also takes some of the visual heat off the tagging system, and I get out the behavior I find most intuitive for areas.

They mention in their wiki that the visual representation of Areas isn't set in stone, so some of this could change before the Beta is released.