I'm pretty sure we've all experience the same hesitation when buying new Mac: snap one up now, or wait until a new model arrives? And when will that new model arrive?
Mactactic tires to eliminate some of the guesswork by estimating a model's shelf life. For instance, right now the Airport Extreme is rated a "buy," as it's brand new, and the Mac Pro is rated "Caution: May be updated."
It's all based on guessing, of course, but still fun.