Microsoft has made a small but significant alteration to the way it sells Microsoft Points on Xbox Live.
North American Xbox 360 users can now purchase the Marketplace currency in increments of 400, to better match the normal pricing of Xbox Live Arcade titles and downloadable content.
Previously Microsoft Points were only available in increments of 500, which meant that in order to buy an 800 Point Xbox Live Arcade title users would actually need to purchase 1000 Points.
So far the Points structure change is only confirmed for North American Xbox 360 users.