Version: 1.1 (using KDE 4.1.0) OS: Linux Installed from: Ubuntu Packages I opened the /home/my_name/.thumbnails/normal folder in dolphin, with view mode Icons selected. I selected all files (more than a thousand *.png) in folder with CTRL+A then I dragged them to the Trash icon in the Places panel. Dolphin started trashing them,the window with progression bar indicated a very very slow progress (for sure it would have taken several minutes to complete the operation), and the dolphin main windows was updated slowly. As a work around I pressed the "Up" button and the operation became almost instantaneous. So i think that updating the main window was slowing the process.
This is related: http://www.kdedevelopers.org/node/3683 ("KDE-4.2 will be 32 times faster deleting a large number of files compared to KDE-4.1"") This bug seems to be a "duplicate" of bug 43356 (as the link says)
*** This bug has been marked as a duplicate of bug 43356 ***