Play It Safe...
I think it's a safe bet to play it safe here all the way around.
Most of this thread has been focused on the "What if's" regarding the update and SIM Relocking due to the explicit "Warning". I think if you have even "Spoof activated" your iPhone using iNdependence (Jailbreak), you should also play it safe and perform a software restore of 1.0.2.
Remember, even spoof activation costs Apple money as they don't get their AT&T cut. Don't be surprised that if you Jailbreaked your iPhone, you end up with a brick as well. I don't think this warning explicitly applies to SIM unlocking. If you read between the lines, I have a feeling this is going to jack a lot of iPhones with various mods.
SO I HIGHLY RECOMMEND even those who simply "Jailbreak'd" their iPhones for spoof activation, SSH/SFTP, interface hacks, etc simply perform a 1.0.2 factory restore until we know more about the 1.1.1 firmware. If those with Jailbreak'd iPhones don't get bricked when 1.1.1 comes out, then you can simply return to using 1.0.2 having the piece of mind that you will be able to update to 1.1.1 and still use your iPhone.
Obviously Jailbreak is probably going to get disabled in 1.1.1, however, what scares me more is that if your iPhone has already been Jailbroken and even returned to Jail, if you don't do a factory restore, will you even be able to upgrade to 1.1.1 at all? I think a few days of pain with this is more than worth it to find out. I would rather have an operational iPhone that can be updated to 1.1.1 and wait for whatever new version of iNdependence that comes out that allows spoof activation in 1.1.1. It's constant roulette, even so, the next update may hose your iPhone. At least until my Verizon plan expires this December, knowing the 411 on 1.1.1 is crucial to me.
The statement orginally released by Apple was a VERY COOL way of saying, we understand, we know what you did, you're a customer, just make sure you're straight before the update. I think this was insanely cool of Apple. They know they got hacked, but business being business, they have to do something about it and they are giving those in the proverbial "Know" a chance to play it straight before your iPhone is "Bricked".