Using SharePoint 2007, charts & graphs were always flattened from 3D to 2D. (referring to OOTB excel services)
This behavior still exists in SharePoint 2010, so please don't expect any pretty 3D graphs using WAC.
The good news is that sparklines are 2D, and those will still look great in the browser!!!
If you don't know what sparklines are, shame on you!
They were invented by Prof Edward Tufte and they are now included in Excel 2010.