I've found that after about six hours, KDE gets really slow. Click a button and it will respond five seconds later. When typing in a field, I can be an entire sentence ahead of what shows on the screen. This is a problem. I degrades even more quickly if the "special effects" are turned on. The work around is to logout and log back in every so often. I don't want to interrupt my work to restart X. Is it KDE or the nVidia driver? Gnome worked fine with this same nVidia driver.
Every so often, a window will become unresponsive. It shows on the screen, but the focus is on some other window. Nothing I do will transfer focus to the frozen window. If there is a modal dialog box somewhere, I don't find it. I can grab other windows and drag them around, but when I do so, it drags under the frozen window. I've yet to be able to get anything above the frozen window. It isn't the same app that freezes every time. It seems that any app can freeze in this way. Is it KDE? likely.
I'd really like the content of panels to be dependent on which activity I'm in. I keep a panel of useful tools on left edge of the screen. The tools that I use in software development are different than the tools I use when I'm working with images. I can't see that this is possible.
I'd like to be able to exploit window behaviors, but the documentation is sparing and hard to find. It seems that the design assumes that the user is a KDE developer and understands the terms, parameters and allowable values. All I want to do is to have one button open eight or so terminal sessions, each with a different color profile and absolute position and size. I can't manage to do that. In Gnome this was trivial.
In the same vein, it seems that KDE apps are imbued with a set of command line options that come from KDE itself. If you get the command line help for 'konsole', you'll find that there is a --geometry parameter that has a similar syntax as the analog in Gnome. Unfortunately, konsole ignores the parameter. If you're going to document a parameter and display it as available to users, then it ought not be silently ignored.
I know nothing about the KDE organization. Is there a company behind it? Are there a lot of contributors or only a small handful?