One of the reasons Apple tries so hard to keep upcoming products under-wraps is something called the Osborne Effect. In 1983, Osborne Computer announced the future release of several new machines that would far out-perform their current offerings. Unfortunately, Osborne was counting on sales from their current machines to pay for production of the next-generation products. As soon as people heard something better was in the pipeline, sales dried up, and Osborne eventually went under. The very same thing would happen if info were to get out about a new iPod or Mac; no one is going to buy an Mac now if they know that by waiting a month they can get a much better one.
The rumor mill however continues to feed that little nagging devil on our shoulder telling us to wait just a few more weeks to see what will be announced. The issue is, there is a good chance that the thing we are expecting to get replaced is left alone, and we will have waited all that time for nothing. And when it comes to the holidays, when gifts are expected on very specific dates, waiting often isn't an option at all.
Lucky for those of you considering the last minute purchase of an Apple product for the holidays, Gizmodo has a quick roundup of purchase safety dates after which you can buy from Apple safe in the knowledge that if Unkie Steve does replace your product at Macworld, you'll be able to exchange it for a new model.