Ok, so I was looking around for this for quite a while. Without finding any info on the subject, I figured a way to do it:
Go into your settings > Account & sync > Choose the Facebook account > Remove Account
then add the account again, give it a few minutes, profit.
worked for me. least, for "my contact card" picture. For just user profile pics, idk. mine updates just fine. It sounds to me like you guys are not staying logged into facebook? idk, just a thought.