TSA PreCheck is the best thing since sliced bread. Even if you're not a member you might have gotten lucky and been sent into the PreCheck line occasionally. Officially you have to apply and pay for membership, but most airports send random people (who are not members) through the PreCheck line to help reduce lines.
The TSA says they are now ending this practice... only PreCheck members will be allowed in the PreCheck line for expedited screening. For members, this means lines should be even shorter and more efficient. Unfortunately for nonmembers, this could mean even longer lines to go through security.