I've been following news and stuff on the kernel, and the day I leave a constant high-speed internet connection (Home for XMas) Linus releases the latest kernel. So I haven't really had the connection to download it and give it a try.
(Me and my friends even had a release party :-D )
2.6, from what I've read, has some very significant performance improvements, and it has been ported to additional platforms. Much more hardware has been added. The merging of ALSA drivers into the Linux kernel is exciting b/c it allows for more professional multimedia stuff. I agree that stopping development on 2.4 is probably a bad idea, considering production systems will probably continue to use 2.4 until 2.6's stability has been proven.
As far as the performance goes, here's what I've read:
NPTL (Native POSIX Threading Library--This has been included in the RH distro since RH 9, and according to benchmarks run by its creator, the new library can create/kill 100,000 threads in about 2 seconds, as opposed to the old I/O library where it took 15 minutes to complete such a task.
The O(1) task scheduler is significant. For you not CS types out there, this means that it doesn't matter how many different tasks you are running, the kernel can scheulde at a constant rate, basically eliminating some scheduling bottle necks that can slow down the system.
I say that this is a very significant move towards using Linux on the Desktop and increasing its hold on the server market. I say this kernel will give M$ some trouble once it has stood the test of time, which may be only a few months.