You should only be limited by what can be manufactured, not what can be modeled.
Stephen Samuel Founder and President of Design Visionaries has just finished a lecture on designing complex shapes with NX. I figured that since Mr. Samuel has been presenting at this conference for the last 15 years and has written a few books about using NX, I should probably see what he has to say.
Briefly, he compared using NX well to playing a musical instrument. It takes a certain amount of practice, creativity and artistry to become a good industrial designer.
The bulk of the lecture was a demonstration on creating a complex shape with NX. Take a look at a consumer good. If the light is reflecting off of it evenly and regularly, the designer knew what he was doing.