Despite all the FUD that KDE4 won’t stay up to the expectations of the users, I must say KDE4 has impressed me a lot. It is definitely a lot more faster than KDE 3.
The shiny new desktop with all the new core technologies of KDE 4 and the new visual effects (kwin, plasma, oxygen), all make KDE 4 the best.
Go ahead and install. It is wonderful.
PS: The KDE 4 Debian packages are available in experimental. The Debian KDE Team has done a fabulous job in bringing them in time with great quality. Thank you.