Nintendo has patented some or all kinds of GB/GBC/GBA emulators. See this Zodiac Gamer forum thread:

http://www.emuboards.com/invision/index.php?showtopic=10975

Will Nintendo go after other developers?

well....they doo have the right:( :( :(

Yes, and this sets a precedent for any other emulated system. Amiga, Atari, Sega, MAME.... could all go down the same path.

Eek.

what is this world coming to:( :(