You need a lot of watts to pop corn or dry hair. If you have a high capacity battery charger for your laptop, then don't let the battery run way down because the little 12v cigarette lighter wasn't intended for long-term use at those watt transfering conditions.
For a small, continuing load, they do work -- within limits.
Power (watts) = Volts x Amps.
Most of these outlets have very low rated capacity in continous use.