Version: (using KDE 4.3.2)
Installed from: Ubuntu Packages
In Nautilus (and I think I remember reading Konqueror too) you can add a list of files and directories to a .hidden file in a directory and they will be hidden. This is very useful for files/directories that have to be named a certain way but you don't ever access them from the file manager and they just get in the way. In particular, some applications installed using Wine will add a configuration directory to your home directory that is annoying. Adding this feature to Dolphin would be great.
*** This bug has been marked as a duplicate of bug 64740 ***