Bats are little rodents with wings. They are as blind as... well... as bats, and navigate through darkened areas via a sonar process called echolocation, which involves emitting sound that vibrates off surrounding obstacles, sending a signal back alerting the bat to its surroundings.
People seem to have a natural and healthy fear of bats. This could be because they are known to carry various diseases like rabies, but there is always the possibility that the bat in your vicinity may also be a vampire.
The opening theme to Scooby Doo showed a flurry of bats scattering across the screen. Bats tended to pop up from time to time in various episodes, scaring the crap out of poor Shaggy and Scooby.
Batman clearly has an affinity towards Bats, as he has taken their imagery as his namesake. Bates tend to gravitate towards the Batcave as well, and sometimes even venture forth into nearby Gotham City. In one such instance, a group of bats got inside the Gotham Exports warehouse, scaring a couple of thugs who worked for Rupert Thorne.