Most others use them with a combination of other law systems and some (including Indonesia, the biggest Muslim country) use them only in family law.
Two things:
1.) Its most important to evaluate what aspects of Shariah law are incorporated into the total body of law, how explicit that incorporation is, and which laws have precedence over conflicting laws. For example, no matter how much English common law is incorporated into their system, Pakistan is still governed by Shariah law where it counts (with the probable exception of interests rates).
2.) You also have to see how the laws are enforced; laws regarding religious freedom (already somewhat deficient by American standards) and religious equality are commonly ignored in Indonesia, and Ahmadis and Christians in most areas of the country suffer discrimination and effectively cannot even worship freely.