If you're a relative newcomer to the Mac (read: halo switchers inspired by iPod/iPhone) then chances are pretty good that you and OS X (Oh-Ess Ten) don't have a very long history together. In fact, switchers who were enticed by the iPod/iTunes ecosystem would likely not have any experience with the Mac prior to 2003.
That being the case, and given the ramp up to the release of Snow Leopard this Friday, it might be a worthy use of time to check out TwistedMac's overview of OS X. It starts with the Public Beta of OS X that was released in September of 2000 and flies all the way through to the current, latest release of OS X, 10.5 Leopard.
A brief description and screenshots galore provide ample coverage for many of the features and nuances of each release over the years. If you have only been using a Mac in this millennium you will find this overview quite interesting and informative. Even if you've been on the Mac since the OS 9 days, it is still entertaining to see how far OS X has come in the past 9 years.
As a relative Mac newbie, I will open myself up to public flogging and admit to the fact that my earliest experiences with Mac OS were in the 10.3 Panther days. Truth be told, I didn't even switch until after 10.4 Tiger was released. Now, however, I'm going to hide out until tomorrow morning when I can purchase 10.6 Snow Leopard while the rest of you give up the goods as to when you joined the team.
Tip of the hat to Evan H. for sending this in!