There are many reasons your electrical outlets could go from being handy to being scary.
The average consumer believes that as long as the outlet is working that it ok.... That may be the one of the biggest misconceptions in the electrical field.
For example, older homes may have receptacles which are damaged or which, otherwise, may have deteriorated over the years. For example, if even part of the outlet's plastic faceplate broke away, the prongs of a plug could bridge from the electrical contacts to the grounded strap, resulting in electrical arcing.
Outlets also deteriorate from repeated use -- everyday stuff, like from plugging-in and unplugging appliances (as is often done in kitchens and bathrooms). As a result, when plugs fit loosely into receptacles, especially the two-prong ungrounded type, they may slip partially or completely out of the receptacle
If your outlets have poor internal contacts or loose wire terminals, they may become overheated and emit sparks. Even a receptacle with nothing plugged into it may run hot if it is passing current through to other outlets on the same circuit. To prevent damage to the receptacles, appliances should be switched off before unplugging from a receptacle.
Have a qualified electrician replace damaged receptacles or those that feel hot, smoke or sparks, those with loose fitting plugs, or outlets where lamps flicker or won't light.
If your electrical outlets are okay now, keep them that way! Don't unplug anything by pulling the cord at an angle. Doing so may break away the brittle plastic faceplate, leaving live parts of the receptacle exposed