I'm sick of people using the excuse "BUT EMULATORS CAN BE USED TO HOME-CODE AND TO TRY OUT GAMES! WHAT THE HELL IS NINTENDO DOING? THIS ISN'T FAIR!"
Bullshit. While those ARE practical uses for emulators, the reality is, those home-coders make up about as much of the emulator users as people who use linux on their home consoles, perhaps less. In other words, the excuse for making your own GBA software is nothing more than an excuse. And if you really want to develop for the GBA, then buy a damn development kit from Nintendo.
And if you want to check a game out, rent it from one of those online dealers which let you rent games, or buy the game, try it out, and return it if you don't like it. I know, a lot of people do this legitimately, but a lot of other people say something along the lines of "After trying the game, I feel it isn't good enough for me to buy," but they go and keep the ROM.
And Ian, developing a device to play GBA carts on, say, a cell phone, would be illegal. It would be like making a device that allowed you to play G.O.D.s on your X-box: Do you honestly think that could be considered legal?