In one of the updates that occurred recently, a new environment variable, QT_PLUGINS_PATH=/usr/lib/kde4/plugins was added. (Maybe it was added as a KDE update rather than a Qt one; I don't know.) This environment variable doesn't appear to be needed. But worse, it causes problems with locally installed versions of PyQt4. On my machine I have Python, Qt, and PyQt4 from the Fedora packages. But in addition in $HOME I have built my own Qt and PyQt4 and Pythons so that I can experiment with them. With QT_PLUGINS_PATH=/usr/lib/kde4/plugins set it takes 13 seconds from the moment of invocation for a PyQt4 file dialog to appear. If I unset the variable (as I now do in .bashrc), the file dialog appears instantly as expected. I realise that not many people will need to install multiple versions of PyQt4 like I do, but I still think the environment variable should not be set unless there is a really compelling reason to do so.
1. This is set by kdelibs4, not qt4. The file which sets it is /etc/profile.d/kde4.sh. 2. This is not a new thing, this has existed ever since kdelibs4 has existed in F8. (And it's the same in the kdelibs in F9 and Rawhide.) You probably simply didn't have kdelibs4 installed before. 3. Your claim that "this environment variable doesn't appear to be needed" is incorrect: it is required for KDE plugins to be found by Qt, including but not limited to: the Oxygen widget style in kdebase-runtime, the Qt Designer KDE plugin in kdelibs4-devel, the image format plugins in kdelibs4 itself etc. 4. What you're seeing seems to be some problem your custom version of Qt 4 appears to have with one of the plugins in that path, which also shows that the environment variable is obviously not unneeded, because something is being loaded from it. ;-) 5. The file is marked %config(noreplace), so you can just hack the variable out if you don't like it. (But I think you should figure out the actual problem instead.) Oh, and it's called QT_PLUGIN_PATH, not QT_PLUGINS_PATH.