This is mostly a geek-read, so let me sum it up for you. The more apps you add to facebook and myspace, the less safe you are. Don’t add people you don’t know well (ouch, log in my own eye) and use unique passwords for each account. This or this may help.
“A quick (and very much incomplete) hall of shame here includes MySpace, LiveJournal, and Hi5, all of which we’re surprised haven’t sunk into the East Bay under the weight of their own pwnability.”