#1. It’s not sanctioned by Apple. Apple has been very careful with how they have developed their hardware, and are very closed about it. When someone develops something for an Apple product and that development isn’t sanctioned by Apple, you run the risk of it not working as it should, conflicting with the device itself, or just all-around bricking that iPhone.
#2.My iPhone just works already. It’s not perfect, no. There are other things that I wish it could do, yes. But… it’s not doing anything that I don’t want it to do. So why mess with something that already works?
#3. There is an SDK (Software Development Kit) coming soon from Apple. This will allow developers to create more things for the iPhone. With the enthusiasm already shown for this, I am confident some pretty cool things will be created in no time, and released.
#4. Hacks can lead to problems. I have done this to other devices in the past. Every time, it invariably either messed something else up, or caused an issue with a future update. I need my device to work, not get screwed up because I installed something the device wasn’t expecting or necessarily designed for.
#5. Wirelesspacket brought up this one. He pointed out that you don’t have a trust system in place when you use something like this. If it’s not sanctioned by Apple, then the trust system you are relying on may not even exist. You’re trusting the hack will do what it says, and won’t cause issues. But you can’t be sure.