I installed KDE 4.1 today on a few of my machines. I'm quite happy with it now, and I will be making the switch from GNOME back to KDE. KDE 4.0 was too buggy to work with. After a few crashes of KDE 4.0 within the first hour of installation, I went right back to GNOME 2.22.
GNOME is fine for the most part, though there were often times I wanted to customize something that I just couldn't do ( dual headed background limitations, running a separate screensaver process per head slamming the cpus, and lack of any customization in the newly, revamped gdm architecture come to mine ). But I digress. For me, KDE 4.1 is stable, looks great, and so far is not lacking any customizations I need. It took a few minutes of figuring out where the team is headed with Desktop folder views. I think they're way cool, and they help one keep a nice, organized desktop.
If you gave up on KDE 4.0 like I did, jump back on! KDE 4.1 shows the dedication of the KDE team to answering issues and pioneering the way for the Linux desktop.