You already knew that Excel can do straight date math, but it can also take into account holidays to find the number of working days between two dates. Tech blogger Chandoo points out the =networkdays(start date, end date, list of holidays) formula, which turns out the number of days minus holidays (and vacation) between the start and end date—quite useful for work project spreadsheets. Chandoo offers several other "hey I didn't know that" Excel tricks too, like filtering unique items from a list, sorting data from left to right, freezing panes, and coloring your worksheet tabs. Excel can be Exciting: 15 Fun things to do with Microsoft Excel [Pointy Haired Dilbert - Chandoo.org]