As seen in this video, the GBA slot on the DS Lite sucks. I don't play many GBA games, but I do like the DS Rumble Pak, which happens to be in the form of a GBA cart. Cabel's first look video/photos are worth a look too.
How could they overlook this? I take design very seriously and cannot fathom why/how they could not fix this problem before production.
Although I will most likely buy one for the brightness of the screen. It is brighter than the PSP screen after all. But I am not going to pay full price for the DS Lite. I may be crazy, but not that crazy.