I have had the same problem - intermittently. It seems to be most common with Google Earth and Google Sky, as well as World Newspapers. But some others have been affected also. When I go to the Applications area of Settings, the apps show as installed, but the icons are GONE! The only fix I've found is to uninstall the app, then install it again - it will reappear and work fine, at least for a while. Verizon folks say they have never heard of this happening, just as they are doing for some other problems I'm having, like intermittent screen shut-down and lock-up.
My apps disappear only from the homescreen. They are still installed and I can access them if I go into the apps menu, but I'm unsure as to why they've left the home.
Sorry, this doesn't help much, but it definitely seems like a problem that's recurring in a number of different ways.
