In Mac OSX 10.8 developer preview, Apple added a long desired feature to the calender.app for business use: calender weeks.
Problem: However, the displayed calender week is one week ahead the real calender week. Typically calender weeks starts with the first full week of the year. But, calender.app starts calender week one in the week with January, 1st. This might be an US/EU issue, but should be configurable in final release.