As far as total worldwide sales I'm pretty sure the DS will sell better than any next gen console. Don't expect much momentum lost until Nintendo's next handheld comes out, and even then the DS will continue to sell well like the GBA did after the DS came out. I don't see any less than 80 million sold when all is said and done, and as high as 120 million is not impossible, though that high end would probably assume Nintendo wouldn't get their next handheld out until 2011 or later. My guess is probably DS 2 will come out 2009 or 2010.