What I see in these screenshots is just exceptional and mind-blowing. But the real question is, "how far will the KDE devs go to realize these mockups?" If the kind of default KDE 4 I am going to get is similar to the screenshots, then believe me, I am going strike-off the iMac entry from my wishlist straight away.

No, don't strike off the iMac, it's a delicious computer to look at and to play with. It's almost a work of art..
Other than that, I have high hopes for KDE 4. Gnome is getting a brush over, but KDE is still the most popular desktop environment for Linux users.
Plus don't forget, Xandros, Linspire and Novell, etc are going to get support from Microsoft in relation to further KDE development.
This article makes some interesting observations in regards to KDE 4 & the future of Linux.
http://www.itnews.com.au/News/64237,why-linux-will-succeed-on-the-desktop.aspxCheers
Aqua