There were several posts (like the one from Jason) on Apple's statement posted yesterday regarding hacked iPhones. Everyone who hacked their iPhone, like I did, shouldn't be a bit surprised by this statement and if you are then you shouldn't have hacked your iPhone in the first place. Hacking the iPhone carries a known risk and I am sure Apple felt some pressure from AT&T to make such a statement. I personally am saving myself US$50/month by using my iPhone on T-Mobile and dropping AT&T, but I also made the decision before I hacked it that I can live with the iPhone the way it is now along with the 3rd party applications I have loaded on it. The iPhone Dev Team who enabled us to SIM unlock our iPhones issued a statement today in response to Apple's statement.
The team stated they are working on a tool that will allow you to undo the unlock of your iPhone and return it to its factory state so you can go back to using it with AT&T and update the firmware. These guys are great and providing this tool is outstanding service. I don't plan to use the tool myself since I am very happy with my iPhone and don't need the WiFi iTunes functionality since I don't buy iTunes music myself. It would take some major update to the iPhone (maybe Exchange sync support) for me to try to undo the unlock, but I doubt Apple will come out with something that blows me away enough to try.
If you have an unlocked iPhone, the best strategy is to wait until the iPhone Dev Team gets their tool up and running. You may then want to wait to see if this next firmware update even causes any problems since there is the possibility that it may not. If this firmware update does relock phones or cause issues, then you can bet that the iPhone Dev Team will start working on another way to unlock the iPhone and the cat-and-mouse game will continue to play out.