Earlier quoted context omitted.
GDocs has been the primary office tool for the past several jobs I've had across the entire staff. What can it not do that office can do?
Within large organizations, I don't think there's any replacement for Excel. Google docs are great as a Word replacement, but Google's spreadsheet offering is a spreadsheet. Excel is an extremely sophisticated development environment.
COM and VBA scripting? Access database sourcing?
Google spreadsheets even has analogies to this functionality (albeit in Google flavors).
It's certainly not the formula and pivot table capabilities which Google spreadsheets has pretty good parity with. At one point in time you could argue that excel handled larger files better, but more recent versions of Google Spreadsheet seem to handle larger files pretty well.