I'm not having good luck at all, but mine is still under a Best Buy warranty, which I'm taking full advantage of. My first two DS Lite's had dead pixels on the top screen. Now, on this third one that I've had for a week, the L and R buttons suddenly stopped functioning at all. I've tried three games. I haven't even flashed or modded the damn thing and it dies!
I'm going to take it all back to Best Buy again today and see what they say. Hopefully there aren't terrible about it, which they were last time. "What do you mean it's broke again?" Grrrr ....
I did have the DSL unprotected in my bag, but there was nothing around to hit it, so I think I'm going to invest in a cheap bag/case for right now, just in case that's what caused it.
EDIT: Took it to BB, and they powered it up and the stupid buttons worked. The R button feels incredibly loose, so they are possibly failing, but they work for now. Kinda upsetting -- hard to play Mario Kart DS if the R button fails.