Seven plus or minus two reasons you should forget the magical number seven plus or minus two
Ron's Ramblings (cool new blog found via Webword) has a list of articles that explain how most people misuse George Miller's 40-year old research on short-term memory limitations.

Some excerpts:

How to improve design decisions by reducing reliance on superstition by Dr. Robert Bailey of Human Factors International (HFI)
"At least partially because of the success of Miller’s paper, the number “seven” is now almost universally and erroneously accepted as the human capacity limit for a wide range of issues."

The Myth of "Seven, Plus or Minus 2" by James Kalbach in WebReview
"While Miller's "Magic (7±2)" principle reminds us of moderation, it is not appropriate for fundamental navigation decisions and leads to an arbitrary "one-size-fits-all" solution. In no event should it be taken as an absolute law. On the other hand, spamming site visitors with hundreds of navigation links is also irresponsible. Feelings of confusion and information overload are problematic. There probably are limits to the number of menu items a web page can display without overwhelming the user, but these do not come from Miller.
Clearly, the optimal number of menu items cannot be reduced to one generalized rule applicable in all situations. Instead, when planning the information architecture of a site, the two most important considerations are breadth versus depth and the display of information."

More in-depth info on the same topic:
3.14159, 42, and 7±2: Three Numbers That (Should) Have Nothing To Do With User Interface Design by Denny C. LeCompte
"The fame of Miller's number would be a wonderful thing if not for a couple of problems. First, at least in private settings, the magical number is often invoked inappropriately. For example, an individual may claim that a web page should have no more than 7±2 links on it. As will be discussed in more detail, nothing Miller said lends support to such a statement. Second, even when it is cited correctly, Miller's work is discussed as if the scientific understanding of short-term memory had not advanced at all in the last half century. In fact, an analysis of Miller's original paper and of subsequent scientific research suggests that 7±2 is no more relevant to user interface design than is Douglas Adams' facetious 42." ... "At best, Miller's 7 ± 2 figure applies to immediate serial recall for a sequence of familiar, easy-to-pronounce, unrelated, verbal stimuli presented auditorily with no distracting sounds within earshot. Thus, the narrow range of generality implied by the research findings cannot support the wide variety of situations to which people try to apply this heuristic. Based on the relevant data, user interface designers should probably forego application of the 7 ± 2 heuristic altogether."

Fighting (with) Hierarchies - Part I: Basics - SAP Design Guild
"Why is breadth harmless and why are the people who cite Miller wrong? Because the user doesn't have to memorize the menu - that is to say, the link list. It's on the screen and available to the user. The memory problem is posed by the levels or steps to be remembered; that is why a route in a maze is so hard to remember."

Of course, as the SAP article points out, good UI's rely on recognition rather than recall, so the idea that users have to depend soley on short-term recall memory is flawed from the start.