The more things change, the more they stay the same, or so they say, and sometimes that's a good thing.
The last thing you want to encounter when doing a software upgrade is having to learn to use it all over again.
Happily, that's not the case with Mac OS X 10.5, a.k.a. Leopard. While the look is a little different, and there's some new features to be explored, chances are just about everything you already knew how to do with OS X still works as expected. It fits like a new glove carefully modeled on an old one that had already shaped itself to your hand.