Excel is the furthest along of all the Web Apps in approaching the suite's final feature set and is currently the only app that lets multiple people work on a document at the same time.
It looks much like the Office 2010 version of Excel (including the Ribbon that users tend to love or hate and the redesigned Office button in the upper left-hand part of the screen). In other words, if you use Excel 2007 or later, you already know how to use the Web App version. Creating a spreadsheet, inserting formulas, handling tables, recalculating the workbook, etc. work exactly the same in the Web App version as they do in the client version. When you import a worksheet, it looks exactly as it does on the client-based version, including charts.
At this point, it's also a very stripped-down version of Excel. There's no way to create or edit charts, for example, and most of Excel 2010's features -- such as advanced formulas, control of page layout, ability to mark up and review spreadsheets -- are missing.
The Office 2010 version of Excel has seven separate tabs on the ribbon; currently, the Web App version has only two, and those two don't have all the features that their equivalent tabs have in Office 2010. However, if you import a worksheet that has a chart, and you edit the underlying data for that chart, the chart will automatically change to reflect the new data, just as it does in the client version of Office.
I ran into a number of problems when I tested this version. I could not paste data or text into a spreadsheet, for example, a problem that presumably will be fixed further on in the development cycle. In addition, I was able to view but not edit .xls files -- currently, you can only edit files in the newer .xlsx format. The same holds true for PowerPoint and Word -- you can only edit .pptx and .docx files.
Excel is the only one of the Office Web Apps that has collaboration enabled, and it worked as advertised. I was able to work on the same spreadsheet on both a Mac and PC simultaneously, and was able to see the changes on each machine made on the other.
However, there is no apparent way to lock the worksheet, which means that two people can work on the same cell simultaneously, overriding each other's work. In addition, when multiple people are working on a spreadsheet at the same time, the undo and redo functions do not work, making it more difficult to get the spreadsheet back to its original form. This is a problem that needs to be addressed in future versions.
The Technical Preview of PowerPoint has fewer features than Excel. Creating new presentations from the Web at this point is rudimentary, at best. You can't, for example, apply themes or backgrounds, use animations between slides, or, frankly, do much beyond creating new slides.
However, adding new slides is exceptionally easy, and works much like it does in the client version of PowerPoint. And as with Excel, when you open documents that you created in the client version of PowerPoint, they look online exactly as they do when on your PC. You can also play presentations as a slideshow, and the presentation includes all the animations and special effects that you created in the client version of Office.
As with Excel, you won't be able to edit files created with an older Office file format -- no .ppt files. Unlike in Excel, when you open a .ppt file for editing, you have the option of immediately converting the file to .pptx, without having to go through the process of saving the file. Still, it would be better if it supported the .ppt format, just as if it would have been better if the Office Web Apps version of Excel supported the .xls format.
Word and OneNote
At this point, there's very little to be said about Word, because you cannot create new Word documents or edit existing ones in the Technical Preview. All you can do is view files. As with Excel and PowerPoint, though, the viewer is excellent -- files look identical to the ones stored on your PC. At launch, Word will lack one important feature of Excel and PowerPoint-- no simultaneous editing.
As for OneNote, it's not yet available in the Technical Preview, and as with Word, you won't be able to work simultaneously with others when it does launch.