Equally impressive were the app's collaboration capabilities. Multiple authors can open the same document simultaneously, and when one author makes changes, all the other browser windows are updated with the new figures in real time. (It's worth noting, however, that Microsoft says a similar capability will not be available in the Word Web app at launch time; apparently there are limits to Microsoft's AJAX approach.)
Notably absent was any kind of revision history like what Google Docs and Zoho offer. It was fairly trivial to corrupt an entire worksheet with a few clicks of the mouse, and given that the document saves itself automatically at regular intervals, the Revert to Saved button wasn't much comfort. Hopefully this situation will improve as the suite matures.
More troubling were the features the suite didn't support. While the other suites generally discarded elements of spreadsheets they couldn't parse, Excel Web App warned me that files containing "VBA, shapes, or other objects" might not import properly. Worse, when such files did load, the presence of such objects meant they couldn't be edited. It seems the complex Office file formats can be a bit much for online applications to handle -- even for Microsoft itself.
The final version of the Office Web Apps will also include a Web-based version of OneNote, but that application isn't part of the Technical Preview and wasn't available to demo.
Microsoft plans to offer several versions of its Web-based Office at launch. The consumer version will be ad-supported and offer similar Web-publishing features as its competitors (including the ability to embed Word documents in Web pages, formatting and all). Microsoft will also offer a hosted subscription version for businesses, with improved document management and workflow features. Customers who prefer to run the suite on their own servers will be able to do so if they buy a volume license to Office 2010.