Gall bladder disease is statistically more common in Crohns patients than in the population as a whole. Overall, there are "five Fs" that also point to gall bladder issues -- Female (it is more common in women), Fair (more common in caucasians), Fertile (more common in women who have given birth), Forty (more common past that age) and Fat (more common in those with weight issues . . . not that I am implying anything specifically here!)
The tests are relatively simple -- an ultrasound to look for stones, and a series of Xrays taken while you receive an IV solution that simulates a fatty meal to measure the ejection fraction, or the percentage and veolocity of bile being pumped from the gall bladder into the small bowel. An EJ under 35 or so is a clear indication of a bad gall bladder, regardless of the presence or absence of stones. The one big health issue with the gall bladder is the potential for it getting infected or from a stone blocking the bile duct, which can make you pretty darn sick in a big hurry and which is usually an indication for immediate surgery. Overall the best thing to do with a bad gall bladder is to get it out.