The iPhone FAQ is reporting that the issue we've seen with the earlier leaked 1.1.3 ROM update holds with the official ROM update. To wit: if you decide to downgrade your iPhone back to 1.1.2 (or even earlier), you're phone will think that your SIM is invalid no matter what. You'll quasi-brick your iPhone. I say "quasi" because it does seem you can safely upgrade to 1.1.3 again.
Anyway, the advice that Phone different has given you again and again still holds true: if you've done anything non-standard to your iPhone, stay the heck away from new updates until the hackers have had a chance to put it through its paces. Then again, the new location feature is super sweet, sweet enough that even if you do love Lights Out, it's probably worth it to upgrade. After all, the SDK is getting released next month.