From Stop Using Excel, Finance Chiefs Tell Staffs:

Finance chiefs say the ubiquitous spreadsheet software that revolutionized accounting in the 1980s hasn’t kept up with the demands of contemporary corporate finance units. Errors can bloom because data in Excel is separated from other systems and isn’t automatically updated.

This is certainly true, but the other problem is that there is no good way to code review formulas and no version control with the ability to diff formulas. This allows errors to sneak in with no mechanism to detect them.