Mike Blamires

Firstly a quick install guide on Kubuntu (see http://www.kubuntu.org/announcements/kde-4.0.php for more detail):

sudo echo "deb http://ppa.launchpad.net/kubuntu-members-kde4/ubuntu gutsy main" >> /etc/apt/sources.lists
sudo apt-get update
sudo apt-get install kde4-core

I have used KDE over Gnome for a long time, simply because KDE is much more configurable than Gnome and with the leap that Vista has taken (not that I can say I like it) I was secretly looking forward to the the KDE response and managed to wait until after release.

Follow up:

Menu

If there is one thing I take away as a positive from Vista it is the menu, although not a new idea (see launchy et al) inclusion in the 'start' menu is just plain good usability. No more scrolling through three tiers of unordered menu, just type and go. KDE has adopted this well, it's quick and has done a great job of presenting what you need quickly.
My only critique would be that the search response should be quicker, so I can type and enter rather the having to wait a second, however, this is minor.

Plasma

The new desktop shell is Plasma and all the panels, widgets (Mac OS widgets can apprently be used) and objects are part of that, it's not great leap, it does the job. If you like your desktop and don't see it as the waste of space of like I do hit Ctrl + 12 and reclaim the space.

Other

"Other" is such a cop out but this is where it gets negative. Sales people selling systems which are all about the user interface like to talk about screen real estate, it's a typical sales turn of phrase that I am unashamedly going to steal just like KDE has. I have none left, the panel at the bottom of the screen is bold black and way oversized, so is the my window title bar, and don't get me started on the how the tabs look in the Bash terminal.
KDE I want my space back, Windows 98 in 800 * 600 is not a good look.
Still I can get that back myself, we all know how configurable KDE is, oh wait no it isn't. All my control has gone, vamooshed.

For me KDE 4 is not ready, it's all too beta. This is version 4.0 it's a bold an ambitious change ultimately, I suspect, for the better but it's not ready for release, there is too much missing. Reading around there is plenty of "this is only the first version in a series" but its missing so much it doesn't deserve the 4.0 release tag it has been labeled with.
The defaults are not great and although some of this can be attributed to the distribution, I am with Jeff Atwood on this one, defaults count, even in a world where your own configuration is encouraged.

I do hope that there are some serious advancements before Kubuntu include it or they may as well skip a release, sit tight and advise people to get plain old Gnome driven Ubuntu in the meantime and hope to god it changes or pack up and go Gnome.

Having said that if it regains that configuration, user control and a good set of defaults it's going to be great. Sadly I'll be following the MS release pattern and, I'll wait for SP1!