Depends.
On the right side, if there is a crack was likely caused by overweighting of the the hinge in the factory, in this case there was nothing you can/could do to prevent it, nor was it your fault yo begin with.
If it is on the left hand side, I believe it is only a cosmetic defect.
Ok, now time to get to the point, the crack on the right hand side will result in a full blown crack.
It will start out as a cack similar to this.
http://waltercrespo.blogspot.com/2006/08/n...lite-crack.html
The the crack will develop and over time (I am giving you around two weeks minimum) it will result in this.
(First three pictures)
http://jonchoo.blogspot.com/2007/03/my-ds-...inge-crack.html
So I propose you try out the following solutions if it ever comes to this.
1. You trash the thing and get a new ds lite.
2. You get a new shell for the ds lite an either attempt to repair it yourself (I recommend you don't attempt this) or get someone else to do it.
3 If you still have warranty, get new one from the shop you brought it at or Nintendo themselves, but be warned, Nintendo will most likely dismiss that it was their fault it cracked and will try and make you pay around $70.