The cool thing about Karmic, is that there are tonnes more new features and changes than just the stock ones that you hear about all the time.
For example, the volume control has a whole new interface, as well as using pulse audio which allows you to control individual channels and individual app volumes.
There have been many extra programs added to the Ubuntu repositories, which makes installing software easier.
The guest session has had a bit of a tweak and is now easier to use and more secure.
There are dozens of bug fixes and a lot of polishing which makes the whole experience much smoother and feel more integrated. A lot of work has gone into consistency between apps.
By default, Gnome in karmic disables icons on buttons, which makes it look a lot less cluttered.
The new disk utility the OP talked about is fantastic. The notifications have had an overhaul and are now much better looking than the new ones in Jaunty (and they were good looking anyway!). The new icon theme is gorgeous. There are now emblems on your bookmark folder icons too.
The install process is sped up, and now has a fancy slideshow to teach you some basics about Ubuntu. As well as that, you can specify if you want an encrypted home folder on install.
NTP support has been improved for syncing your system clock with web servers. The integration between Gnome and Empathy/Pidgin and Evolution has been greatly improved, with notifications for when you get emails and new instant messages.
The Games menu now has a sub-menu called "Logic" that cleans up all the gnome games.
There is more hardware support, and better support for graphics chipsets from Intel and ATI.
Along with all these OS changes, there comes a tonne of improvements in the default applications, such as Firefox now being 3.5.2, and OpenOffice 3.1.
... and much, much more!
Overall, it's a huge release really. They've compromised well between new features and bug fixes.