The DS came out Holiday 2004, and it has been more successful than any other handheld (at least since the original Gameboy which was also supposed to have passed 100 million in its time).  And unlike some other highly successful video game systems, the DS has had tremendous commercial and critical success with a console that's game library has been considered to be able to compete with just about any other game system's library and it has seen the release of  quality games in almost all genres.  It has even been considered to have been responsible for bringing back once mighty genres like the adventure genre that have lain devoid of highly popular games since the end of The Golden Age of PC Adventure Games in the early 1990s.

     However, eight years is starting to get a bit deep into a game console's lifetime and it might have just seen the biggest game release that it will ever see in Dragon Quest IX in Japan.

    How much longer do you think it will be before Nintendo decides to replace the DS line with an even more powerful handheld like a Super DS or DS Advance?

2012? maybe, the DS is still selling amazingly well, their is no need to bring out a new DS or Game Boy

maybe 2012?

the bigger question for me is what will nintendo have to offer for their next handheld.

The GB lasted a decade, the DS probably will too.

2013 or 14 at this point I cant see nintendo making another handelheld till the ds drops off in sales

2011 at the earliest. 2012 is more likely though.

2012 and i hope its more powerfull than the gamecube.

Probably around 2012. It's still selling like hotcakes.

What reason does Nintendo have to release a new handheld? Currently the DS is (amazingly) dominating weekly/monthly/annual sales charts in HW and SW. The DS is just as strong now as it was when it launched. With the success that the DS currently has, I wouldn't be surprised if Nintendo pushed the lifespan of the DS out past 2012.

I would actually be willing to bet that the 360/PS3/Wii will see a successor before the DS.

2014.