Window icon (pixmap)
When I set GTK theme VLC icon is not changing.
I have no desktop environment like Gnome or KDE. In Gnome, for example, gnome-settings-daemon is setting icons for gnome panel. But it's their own hack to avoid themes ignorance of applications.
According to major policy, application should look for it's window border icon (pixmap) in theme folder, described in ~/.gtkrc with icon name, described in /usr/share/applications/.desktop.
Unfortunately VLC is not following this agreement. As a result some panels, like tint2 or lxpanel get their icon from window border and display it scaled, which looks not very nice.
It's a known issue. There are bugreports in many programs, but not all of them want to fix it. Firefox developers fixed.
Example (tint2, Faenza theme) http://imageshack.us/photo/my-images/52/vlcat.jpg/
Here icon should be squared, from Faenza theme.