Andy Baio Writes About Settling Out of Court Over Pixel Art Depiction of Miles Davis
If you're borrowing inspiration from any copyrighted material, even if it seems clear to you that your use is transformational, you're in danger. If your use is commercial and/or potentially objectionable, seek permission (though there's no guarantee it'll be granted) or be prepared to defend yourself in court.
Anyone can file a lawsuit and the costs of defending yourself against a claim are high, regardless of how strong your case is. Combined with vague standards, the result is a chilling effect for every independent artist hoping to build upon or reference copyrighted works.