By default under KDE, Debian 6 indexes files using
nepomuk which can be suspended on the desktop, but that is only valid
for one session. If you reboot then you have to suspend it again, so I've been looking for a way of turning it off
And here it is - at the menu choose
Settings -> system settings -> advanced tab -> desktop search -> disable Nepomuk Semantic
This kills it dead and should last until you either turn it back on again or you reinstall!