Recent software and firmware upgrades for the iPhone are causing hacked iPhones to "brick".
If you've unlocked your iPhone to use it on a network other than AT&T, then recent firmware "upgrades" might make your iPhone unusable. And if you hacked your iPhone to add 3rd party applications, then you might find that those applications no longer work after the upgrade.
That's because Apple wants to keep you on the AT&T network, because Apple skims something like 30% off your AT&T phone bill each month.
But in the US, how many people are going to unlock their iPhones and switch networks? The only other GSM carrier is T-Mobile.
I think Apple should follow the example set by Palm with the Palm OS. This operating system is ancient and has never been significantly improved. But it's still the best OS for a PDA/phone because of the thousands of free 3rd party applications written by enthusiasts.
If thousands of Apple fan boys are happy to write applications for the iPhone, then Apple should encourage them by hosting an iPhone developers conference.