We've started using the RadControls DatePicker for a site we're developer, and we've noticed that the DatePicker is calculating the week number incorrectly. It's easiest to see the cause of this problem if you look back to the start of the year. According to the ISO standard for week numbers (available here: http://en.wikipedia.org/wiki/ISO_week_date#Calculating_the_week_number_of_a_given_date
) the first week of the year is the week that contains the first Thursday. However in your calculation the first week starts with the week containing the 1st day of the year (it appears).
We would appreciate this issue looked into and hopefully fixed, as it is resulting in inaccurate data entry for our staff who use the DatePicker to find out the current week number.