How many times have you seen your friends or family post on twitter where they're vacationing at, or taking quizes on facebook or myspace disclosing personal information such as maiden name, first school, first pet, first love, birthdate? People are way too careless with their personal information and with the tidbits posted here or there that information can be used to social engineer passwords or even give up enough information to allow for easy identity theft.
Grab yourself this awesome t-shirt showing cause and effect of social media engineering.