I prefer to stay "Low Tech" when it comes to my personal property.
The iPhone still has it's security issues, and I would not trust it to keep my information safe. The apps are not 100% secure, and have seen horror stories about people getting their data stolen, exploited, etc ....
If you trust your personal property to an iPhone ... so be it, but you won't catch me doing it. With the iPhone ... anyone with a WiFi connection and the 'know how' can duplicate your images, phone book, personal docs, etc ....
I think you are being a bit naive in thinking the iPhone is secure for personal information. Would you trust your computer to the internet without a firewall or antivirus? Then don't trust an iPhone with anything other than images you don't care to share with everyone and phone numbers.
Here's what a 2 second Google search brought up....
http://www.mobilecrunch.com/2010/02/...aw-discovered/