Microsoft Office Web Apps are online companions to Microsoft Word, Excel, PowerPoint, and OneNote, enabling people to access and do light editing or sharing of Office documents from virtually anywhere. Office Web Apps is available to consumers and businesses through:
To understand the user experience and features in both cases, you can refer to Using Office Web Apps in Windows Live and Using Office Web Apps in SharePoint pages in the Office 2010 product information and support website.
If you want to experience Office Web Apps features but do not have enough infrastructure, you can log on to SkyDrive and try it out there for free. Just upload a document in the SkyDrive or try creating a new one. You should get a prompt for activating Office Web Apps for your account if not already enabled.
From Office 2010, you can also save a document directly to the SkyDrive. So, no need to save the file to your computer first.
Only thing to keep in mind is that not all Web Apps scenarios are currently available in SkyDrive. For example, you cannot create/edit Word documents. You would get a "Still to come..." message on the screen in such cases.
Microsoft Office Web Apps Deployment Resource Center
Microsoft Office Web Apps Deployment resource center has been launched recently which provides tools and resources for IT professionals planning to deploy Office Web Apps in a SharePoint environment.
The Understanding Office Web Apps and Introduction to working with Office Web Apps provide a good technical background before you start the Office Web Apps deployment in an enterprise. Refer to the Deploy Office Web Apps (Installed on SharePoint 2010 Products) article to learn to deploy Microsoft Office Web Apps.