The real question is, who do you want your data to be secured from? Your typical snot-nosed TSA agent certainly isn’t going to have a device capable of scraping data off of your phone, however both hackers and government might. If you jailbreak your device, it’s possible that a much larger pool of people will as well.
I never assumed iOS was that secure, but not storing Keychain passwords in encrypted files is worrying to me. (Note: I have no clue why I had that in there as it is clearly not consistent with this article, sorry. -Ben) I think the above just about sums up all computer security though. The more you hack, the larger the potential to open up more security holes. However, the pool of people that can exploit and get a hold of your data, is small, but growing. They have to have good reason to want your data.