I hate to be the bearer of bad news but facebook is very public despite people thinking only "friends" can see their pages. So please be careful what you post. People lose jobs or never get interviews because of their facebook pages. It drives me nuts to see what some of the people I know post on the net. Also, once something is posted anywhere on the net (there really is no delete function, no matter what software you have running) someone can access it because there is always a loophole and a printer somewhere.
Most people don't realize how easy it is to access information of any kind. There are readers that retrieve credit card information from unknowing shoppers from outside the store. You don't have to have someone steal your card and find your PIN number anymore. One of the easiest is when people drive around looking for open wireless hubs and hack into home networks, etc.
Unfortunately, I think we were probably more personally secure before the great "techno revolution". I am as guilty as the next person about not changing passwords, but you really should on important accounts every week.