If you're wondering when the best time to buy an Apple product is, the buying guide at MacRumors' will help you make a strongly educated guess.
The buying guide shows you basic information about the product as well as the release history for that product, days since it was updated and average days until update for that particular product. In addition it has a buying recommendation, notes, and a list of recent rumours about the product if you want to delve in a little deeper before purchasing. The example picture above shows the Mac Mini which was recently updated and gets the green flag. The iPhone however hasn't been updated in almost a year and the buying guide recommends waiting out the first half of 2009 for the release of new storage chips.
For more recommendations and a slew of rumours about future Apple releases, check out the link below. If you need a product right now, well then you need it right now. If you've got some time to kill before an upgrade, the MacRumors' buying guide will give you a clearer picture of what you're waiting for.