I have a list in SharePoint with a number of data points. I want to
create a pivot table and charts with that data. I can do that easily
in Excel 2007 but I want to display these within the portal itself
instead. (Users don't have Excel 2007 yet.)

However, when I try to view the Workbook after publishing successfully
with Excel Services, Excel Services tells me it is "unable to load
workbook" because "The workbook that you selected cannot be loaded
because it contains the following features that are not supported by
Excel Services: SharePoint lists"

So I can graph and chart data from other sources to be displayed within
the portal but I cannot do the same for SharePoint data? For that, I
have to use the Excel client??

Are they serious?