Hi, running Ubuntu 12.04.1 LTS here, with gnome-classic (with desktop effects), and compiz 1:0.9.7.8+bzr3121-0ubuntu1.
I am using the static application switcher, in the 'Show icon only' mode. The problem I have is that some applications seem to be using an incorrect, or, even worse, no icon at all. One example is VLC, which when ALT TABbing, shows a rather ugly icon (scaled up to 96 pixels from a lower resolution). But there is quite a few other applications, which don't have an icon at all in the switcher. Here one example is UXTerm, another is Mumble, or dconf Editor. I think I have seen more apps without an icon, and it doesn't work for my custom PyGTK app that I use on a daily basis.
From my investigation, it looks like the problem isn't related to the static switcher only, it occurs in the other compiz switchers, too. Now, it seems to me to be a problem somewhere in compiz, because application shortcuts (the .desktop files) seem to work just fine. That would mean that the icons are in the correct places (within the theme subfolders, like /usr/share/icons/gnome or /usr/share/icons/hicolor). Also, the problem only occurs in the switchers under gnome-classic, and it is visible especially in the 'Show icon only' mode. Under Unity the ALT TAB menu works fine.
Finally, I was able to reproduce this behaviour on another laptop running the same version of Ubuntu and compiz, under gnome classic (with desktop effects turned on).
I am attaching a combined screenshot of the ugly VLC icon, and no icon for the dconf Editor.
Status changed to 'Confirmed' because the bug affects multiple users.