When "gnome-session" starts up to restore the user's desktop, it has a static list of icons for all the applications is knows about. For the ones it does NOT know about, it looks in /usr/share/icons/gnome/48x48 and its subdirectories. If nothing is found, it stuffs in "gnome-unknown.png". This has the added side effect of leaving the splash screen up for way too long, which is annoying because you have to click on it to make it go away. In particular, two icons are missing which correspond to applications that are part of the default Gentoo Gnome startup session. They are "sound-properties.png" and "gconfd-2.png". Also, "gnome-session" does not emit any error messages as it hunts around for icons. This should be fixed in the file "splash-widget.c".
i never see gconfd-2 started up by gnome-session on the splashscreen, nor sound-properties. What version of GNOME are you using? Does this still occur with 2.6?
Fixed in GNOME 2.6