After my horrible disappointment with its direct predecessor (KDE 4.0), I had switched away from the desktop environment in favor of its competitor, GNOME. GNOME served as a powerful, but quick, environment until I began to see its weaknesses. For a while, I debated on whether I should return to the environment that I was more experienced with, or stay in my unfamiliar realm. A few months later, I read a review on the successor to 4.0 and decided to give KDE another try. I decided to do a fresh install of Kubuntu 8.10 and was found that every single issue I had with 4.0 had been fixed.
KDE 4.1 adds greatly improved speed and functionality, as well as stability, into the desktop environment. The major update included some interface enhancements, faster speeds in Dolphin, and (my personal favorite) Folderview. 
This version adds a few interface components similar to Mac OS X, but keeps its own distinctive GUI.
It’s also great for developers because of its inclusion of KDEvelop and KATE. Kontact adds convenience to organization by combining a calendar, RSS feed viewer, journal, to-do list, and e-mail client into one application.
In short, 4.9/5.