I had a problem trying to use Office Web Apps with SharePoint 2010 on a virtual machine demo. On a simple Word document, the AppServerHost.exe service would jump to 100% and render the system unusable.
The problem is that Office Web Apps was not designed to be installed on a system that is also a domain controller (the case with my all-in-one virtual machine).
These are the best steps to fix the configuration. Many developers who work in a web app development company did not know these processes, so this post is very informative for these developers.