AFAIK, nobody has written a perl-interface to the Qt libs. You seriously need that before considering writing perl GUI stuff for KDE. The problem is that Qt relies havily on macros for their slot mechanism. I think it will be messy to translate those to perl. You'd better stick with GTK, as it looks reasonable under KDE. The drawback is that you can't use the KDE ipc. If you want that, you're limited to C++ for now.
BTW, I didn't say you shouldn't use glade. It's just that around here nobody seems to use it. I tried it once, and I was impressed by the amount of perlcode that was generated by quickly clicking a window together. Too impressed actually to work with it :-).