Any injury with its own Latin name can't be a good thing, and this is no exception. Plantar fasciitis occurs when the ligament supporting the arch of your foot (the plantar fascia) becomes strained. The major sign that you've fallen prey to this injury is if your feet hurt or are unusually stiff after periods of inactivity [source: WebMD].
Overtraining is a leading cause of this ailment, though overpronation in your stride is a large contributor as well. Another contributing factor is weight. Overweight people are also prone to this problem due to the strain they put on their arches during normal walking. If you're running to lose weight, you need to be particular careful to avoid this injury.
To alleviate this problem, try stretching and anti-inflammatory medicine, though surgery is an option in severe cases.
You can help prevent this from happening at all if you make sure you have enough support in your shoes before you start running.