Tony has hit it right on the head. Sensitivity is a major characteristic. However there is more than just CMOS vs. CCD. One should also look at pixel well depths and interline vs full frame. If you look at SBIG's site you will notice they have a combination of interline and full frame cameras. Full frame delivers better results, but it hasn't stopped many still using interline (found in the STL11K)
You may wish to check out Kodak's site for more info:
http://www.kodak.com/US/en/dpq/site/...esRoot_product
While your there, check out this monster;
http://www.kodak.com/US/en/dpq/site/...-39000_product
39Megapixel full frame download CCD chip with a 6.8µm pixel size. You'd cover an incredible amount of sky with one of these attached to an astrograph. Crazy stuff.
