I came across an excellent KDE application – BasKet (KDE-Apps entry). It can sit in the task bar and accept drag-n-drop objects (anything from text and URLs to pictures and sounds). These objects can be organized in several tabs. The convenience of it is that one can use it as a combination of application launcher and knotes. Try it, you won’t regret!
The only missing feature I see now is that it does not accept drag-n-drops from Firefox, but that is something to do with KDE as a whole rather than BasKet itself.