This is for those who have not gotten the over-the-air Gingerbread update for their MyTouch 4G.
First, download the file named PD15IMG.zip from this site
and place it on the root of your SD card (meaning not in any folders, just dropped onto the SD card)
Then, turn your phone off. Do a battery pull, or turn off "fast boot."
Hold down the power button while holding down the "volume down" button.
This will boot into your bootloader, where you can select "Apply Update.zip"
Follow on-screen instructions, and enjoy the official Gingerbread on your MyTouch 4G.
DISCLAIMER: Even upon successful install, you WILL lose your settings, apps, and possibly contacts (depending on how you have them stored). I am not responsible for your device if this does not work for you. Also, neither is the original file host. This is not my file, or website. I have had no contact with the original host. I took a shot in the dark, said "screw it" and tried the update. I did successfully update using this file.
This file will update your MyTouch 4G (HTC Glacier) to:
Android Version: 2.3.4
HTC Sense Version: 2.1
Software Number: 2.19.531.1
Kernel Version: 188.8.131.52-g225de41
Baseband Version: 184.108.40.206U_26.11.04.03_M
Build Number: 2.19.531.1 CL95282 release-keys