Welcome sumuk and OptyMyStix...
Alot of the new stuff in Longhorn will probably come under the hood.. performance and capability enhancements to the kernel.. increased security features.. updated and better performing TCP/IP stack.. other enhanced networking features..
One thing I saw a few days back was the way longhorn will handle hardware changes such as a mobo swap. It will actually run a quick hardware detection wizard like that of when the OS is initially installing, everytime the system starts. So it should reduce or eliminate those pesky blue screens when a big change in system hardware is made. That is a nice feature for tweakers/sysadmins in itself.
Most of the work on NT/2K/XP thus far have just been in establishing a good base.. NT the first major test of the kernel.. 2K the first implementation of a good server (AD/DNS/IIS5). And XP just made a few tweaks on 2K, updating the GUI, adding a few features for Home users, and generally making the OS slighly more user friendly. Now MSFT can concentrate on other things.