I just upgraded to Chromium 12 using daily build ppa. But Chromium is still showing older icon on the gnome panel and appication menu. But it shows new icon if I create shortcut on the desktop and it shows new icon about window of chromium. I tried to remove it completely and re-installed but no use. I even deleted the .cache folder from my home directory.
Remove the old icon on the launcher and put the new one bck by starting chromuim it back it i did this with google chrome dev on ubuntu 10.10 (on docky) that helped for me.