If you look at no other material (not even Apple's own web pages) about the latest version of the Macintosh operating system, Mac OS X 10.5 "Leopard," which came out on Friday, then read John Siracusa's 17-page in-depth review. It tells you everything you need to know and more, just like the ones he's written for every previous version of Mac OS X going back seven years.
UPDATE: I should have made it clear beyond my geekery tag that this is a Mac OS review only for a certain type of user, of which I am one. To quote:
While the casual Mac user [i.e. normal people - D.] will gauge Leopard's worth by reading about the marquee features or watching a guided tour movie at Apple's web site, those of us with an unhealthy obsession with operating systems will be trolling through the internals to see what's really changed.
I fully count myself among those with an "unhealthy obsession with operating systems"—people like this guy. Hell, I laughed out loud in public at a joke about font rendering (!) in the command-line Terminal (!!). In the chemotherapy lounge at the B.C. Cancer Agency, even (!!!). If that doesn't seem out of line to you, saddle on up.