This article is mainly a translation of my correspondung German article. However, as I used the German version of Office 2010 for taking the screenshots and this will not be really suitable for my english speaking audience, I will first change the display and help files language in Office 2010 from German to English. This can easily be done, as the language packs are now available. Thanks to my friends on Twitter for this info.
Then I will check out the new Excel 2010 functions NETWORKDAYS.INTL() and WORKDAY.INTL().