Ok, now I'm curious enough to make a post about it.
I'm currently running Slackware 10, although I can recall having this "issue" with 9.1 and 9.0, possibly also with 8.x.
Yesterday I installed an application (Maple 8) and added a shortcut to the K menu. When launched from this shortcut, Maple starts up very quickly but the mouse pointer remains busy, displaying the launch feedback animation, for 30 seconds. During this time, Maple seems just a bit unresponsive, but afterwards it behaves just like it should. Now if I start Maple from the console instead - using the very same command as used in the K menu shortcut - it also starts up very quickly, but with no "busy cursor" whatsoever. It just loads and is done, like it should be.
This has previously occured with other applications as well; in 9.0, it occured when launching Mozilla, for example. Also note it only happens in KDE.
I'd really like to know what's going on. Anyone care to explain?