How popular is the new Kinect motion-based gaming system for Microsoft’s Xbox 360? In 25 days, it’s already sold 2.5 million, according to data it revealed today.

Microsoft originally hoped to sell 3 million by the end of the year and 5 million by the middle of next. Based on first day sales and preorders, the company raised its expectations to 5 million by the end of the year, and seems to be on track with meeting that goal. Retailers seem to agree.

“We expect Kinect will be a must-have gift this holiday season, so Target will continue to receive consistent shipments of Kinect throughout December,” said Target VP of merchandising Nik Nayar in a statement touting the sales figures.

Movement of the new platform should also help sales of the music-based games available for it at launch, most significantly the dancing game “Dance Central” from Rock Band creators Harmonix and MTV.