Actually I was under the impression that Excel was the Emacs(I'm an emacs users :) ) of the non power users. They spend their entire life in there. If Microsoft would just embed IE into Excel(I know someone will point out how this is already happening ;0p) then they would never have to switch app.
My dad spends minimum 4-5 hours of his day in Excel. He's an accountant and uses it to organize all types of info on clients.
On the other hand I almost never use excel. About the only time (and I use google docs anyway) is for managing bills.