From Bryan Bell referencing this post by Marc Canter.

The Third option is Mac OS X. I just finished installing 10.3 and I might have found Nirvana! Everything is fast, and easy to use. Expose has already changed my life for the better.

DiveintoOSX.org has a great blow by blow article on 10.3. It chronicles a lot of the 150 changes in this latest version.