In the six months leading up to September 30, 2009, Nintendo sold 11.7 million DS units worldwide. In the six months leading up to September 30, 2010, that figure has dropped by nearly half, to 6.69 million.
It's to be expected, of course. Not only is the DS getting a little long in the tooth as it approaches its sixth birthday, but with the 3DS now at the forefront of people's attention, interest in a soon-to-be-outdated handheld was always going to wane.
Wii sales were also down, from 5.75 million at the same time last year to to 4.97 million over the past six months.