On the Exchange team, it’s always important to us to get feedback from our customers on what we’re doing well and what we could be doing to make the experience better for you. In Exchange 2007, in response to one of the biggest Exchange 2003 OWA feature requests, we introduced WebReady Document Viewing. This let OWA users preview attached Microsoft Office documents and PDFs in a web browser without having to save them to disk or open them in a locally-installed application. We continued to offer this functionality in Exchange 2010, but we received a lot of feedback that text and formatting of Office documents were sometimes not the same as the original document when viewed in the desktop Office client applications.
We’re excited to announce an update to OWA in Exchange Online that now integrates the Office Web Apps into the attachment previewing experience for Word, Excel, and PowerPoint files! Along with continued PDF support, this means Exchange Online users get high-fidelity previews of Office documents on the web, in exactly the same format they were created. WebReady Document Viewing is perfect for quick document previews and if you need to edit a document you can easily open the file in your desktop Office client from the Office Web App through a single click.
Click on the “Open in browser” link you see next to Office document attachments to start using this feature in Exchange Online today!
Original post @ http://blogs.technet.com/b/exchange/archive/2011/10/31/introducing-office-web-app-integration-with-outlook-web-app-in-exchange-online.aspx