I'm sure you no longer need this information since the post is years old now, but I'll provide a solution that worked for me in case anybody else has a similar problem.
I am currently running Fedora 14 and gnome panel 188.8.131.52.
Follow these steps to restore the gnome volume control applet and its associated icon:
1. System > Preferences > Startup Applications
2. Scroll down until you see Volume Control and check this applet. If you don't see the Volume Control as an option then click Add and provide the following values:
Name: Volume Control
Comment: Show desktop volume control
3. To actually see the icon that allows you to control the volume make sure that the Notification Area applet is also added to the panel: Right click panel, Add to panel, Notification Area.
If the gnome-volume-control-applet was already running then you should now be able to see the Volume Control icon. Otherwise restart your system and then you should see it.