There's been a lot of "will they / won't they" discussion and speculation regarding exactly what players will be allowed to do in the online portion of Mario Kart DS.  Will Battle Mode be available?  How many tracks will be playable online?  How are friends added to the Friends List?  How can players choose whom to race against?  IGN breaks it all down and provides the good news and the bad news regarding the final version of the game.  Here's just one of the many bullet points from their list:

Mario Kart DS does not allow for specific match-ups. Let's say I want to play my friend MrKori and only MrKori in a one-on-one race. The only way I can do that is if I make sure that he's the ONLY person on my Friend's List (meaning, I've physically deleted everyone else), and he's logged on and searching at the same time under the "Friends" search setting. You also can't force a two or three player race. The server will automatically give up and let two or three players race if it can't find a third or fourth player to match up, but players don't have the option to go ahead without the additional racers.

There's a lot of disappointment to be found here.  So many aspects of online gameplay in general are missing here.  We can't specifically choose our opponents or invite specific people to race on demand.  The online tracks are "dumbed down" a little to reduce lag (which is understandable, but still...).  There's no online Battle Mode which I think is the biggest let-down here.  Granted this is Nintendo's first step into online gaming and they had to meet the November 2005 ship date which usually means cutting some features as the clock runs out, but somehow I expected more.  It looks like organizing structured tournaments just became a whole lot harder.