If you hold down the option key on a mac while pressing the Restore option on iTunes, it gives you the option of choosing which firmware file on your computer to use for the restore.
The 1.0.2 firmware is available at:
http://content.info.apple.com/iPhone...8_Restore.ipsw
use Firefox to download it, so that Safari doesn't automatically decompress it. You will need to select the compressed .ipsw file in iTunes to perform the restore.
I tried this with my new iPhone to ensure that I would be able to restore to 1.0.2 even after 1.1.1 is released. I hope this addresses some of the concerns people have expressed in this thread.