information Week article discusses the challenges associated virtualizing applications in the cloud:
Application Virtualization Challenges
'Golden images' quickly diverge from their pristine initial condition because of:
1. OS patches
2. Application updates
3. Configuration changes
"Applications, once released into the wild, tend to quickly diverge from the golden image"
"The difficulties face by developers and systems admins in deploying apps to the cloud are reminiscent of those encountered transitioning from mainframe to the client/server era"