I once wrote a (very complicated) spreadsheet in Excel to calculate bonuses for drug peddlers at a pharmaceutical company. The problem screamed for a database, but the algorithm for calculating the bonuses was so complicated that it as a royal pain in the ass when I tried it. So I ended up with a fugly spreadsheet that still works 5 years on.
The ridiculous thing was that it could've all been well approximated with an exponential function, but that idea was a big no-no. The bonus algorithm is sacred.