The Office Web Apps, OWA, in SharePoint 2010 is a great way to enhance the SharePoint experience. It allows users without a decent OS or a locally installed Office client to view and edit Word, Excel, PowerPoint and OneNote documents.
When you install and correctly configures Office Web Apps (yea, can be a bit of a hazzle if you like me avoid the Farm Configuration wizard) and then enable the required Site Collections feature a cache will be created.