Man, I have to disagree with the statement that Mario Kart DS online is broken! I still think MK: DS is the best game out yet for the DS and I play it online on a regular basis.
there seems to be more people playing MK: DS online these days as it generally takes about 2 minutes to find a race with Rivals, and I find a full set of 4 players much more frequently than when I first got the game. Snaking is annoying, yes, but can be beaten with good driving. And I'm experiencing fewer people dropping out of races than when the game first came out. My win/loss ratio currently stands at something like 60wins/10 losses, so mathematically I can't be experiencing overwhelming dropouts.
I'm just sticking up for MK: DS online experience because I enjoy it SO MUCH. OK it's not perfect, but it's pretty damn close to my idea of heaven on a handheld.
I enjoyed it until the majority of players started snaking. It is next to impossible to beat a beat snaker without snaking - and I find that resorting to snaking saps all of the fun out of the game. That, of course, doesn't stop Mario Kart from being an excellent single player racer and a great local multiplayer racer.
If snaking wasn't an issue, Mario Kart DS would be up there with Tetris and Clubhouse Games as one of the best online DS games.