Microsoft really needs to rethink their decision to do away with the close button in Metro apps. In my Windows 8 virtual machine, I have up to 2GB of physical memory allocated (I know it's low, but I have two 2008R2 VMs running too). I was checking out the sample Metro apps, and I must have launched 3 or 4 of them. The memory demand shot up to about 3.5GB. Windows slowed down to a crawl, and the UI was completely unusable (I couldn't even launch Task Manager) until the running apps somehow shut down by themselves.
yeah i think by rtm they will have to add a "close button" "charm" to the standard set for the times when you really do want the app to close. for example if the app is not working quite right , not totally broke but just has a problem and you do not want to re-start or go to the desktop to find taskmanager.