Cruise Control Can Be Dangerous on Slippery Roads
http://www.snopes.com/autos/techno/wetroad.asp
According to the Insurance Corporation of British Columbia's web page of tips about driving on wet roads:
The only way to stop this wheel-spin and maintain control is to immediately reduce power. However, an activated cruise control system will continue to apply power, keeping the wheels spinning. By the time you disengage the cruise control, you may have lost control.