For anyone interested about the nitty-gritty of the 10.4 update and willing to spend a significant amount of time reading about it, I direct you to ArsTechnica's Mac OS X
10.4 Review in all of its 21 pages of glory. It's a very good, very informative read about not just what's new on the outside, but what's new on the inside as well.
Good luck getting through it!
