In case you're curious, here is what the Excel Web App looks like on an iPod Touch. Note: when rendered in mobile Safari, you do not have the option to view/edit the file in Skydrive, but if you click on its icon, it opens the file as follows:

Unlike on the various desktop browsers (including Safari), there is no ribbon--no UI at all really, except for the contents of the worksheet.
Here is a Word doc in Safari 4.0.3 on Windows:
Here is the same document on the iPod in landscape
Here is the same document on the iPod in portrait:
I also thought I'd test one of my favorite new features of Office 2010: Sparklines! Here's an Excel worksheet with sparklines rendered in Safari 4.0.3 on Windows (note: the Excel Web App does indeed support both sparklines and conditional formatting):
And here's a screen cap of the same worksheet on Mobile Safari (sadly, no Sparklines and no Conditional Formatting/Heat map):
Completely unrelated, but while we're on the subject of conditional formatting and sparklines, the Excel Web App does supports editing these as well. That is, on the above worksheet, if you change the value in cell A1 to 50, A1 will turn green and the sparkline in F1 will redraw with a peak at the beginning like so:
Labels: iPhone, iPod Touch, Microsoft Excel Web App, Microsoft Office Web Apps, Microsoft Word Web App, Office 2010 Web Apps, Sparklines