I can't see how a hacker is going to get into my iPhone - or indeed, how not being jailbroken would make any difference in my case anyway.
If you can't see the difference and thus don't fully comprehend the dangers involved, then you should not have jailbroken your phone.
I'm sorry Keef, what I'm saying is not a "broad generalisation" ... its a cold hard fact.
All it'll take is for a momentary lapse of your awareness ... downloading the "wrong" App ... clicking on the "wrong" link... visiting the "wrong" website. Jailbreaking a phone opens up a number of new vectors that are not present in an unbroken phone. You can't even really trust the developers of the jailbreak software itself.
Apple don't implement jails on their devices to piss you off, they implement them as a part of a rigorous security model, which has been proven to work time after time.