Like Ryan Matthew P., I went to DP for the Pompeii Exhibit.
It is mostly a children's museum, but it is still fun for an adult to play with the ropes and pulleys, and look at stuffed bears and such.
The Pompeii Exhibit was awesome. The layout and lighting created an extremely somber mood to gaze up the plaster casts of dying people.
Don't make this place a primary destination if you don't have kids. However, if you have some time to kill in downtown Charlotte and $20 is burning a hole in your pocket, The Discovery Place may be of assistance.
BTW check out the MILF in the photos!