Saw this on various forums... the RC8 downgrade is avaliable too. been waitinf for this.
Now its possible for people to get root if they have upgraded to OTA RC30!
Follow these steps
1. Format the SD card to FAT32 mode
2. Copy image file XXX.nbh to the SD card and rename to DREAIMG.NBH
3. Turn the device power off and insert Diagnostic SD card
4. Hold Camera button, and press Power button to entry Boot loader mode
5. Press Power button to start upgrade procedure
6. After finish, perform the soft reset to reboot
using this file http://www.megaupload.com/?d=31K3JS3S
After you have done that, go to this page to install JF modified RC30 1.3
http://forum.xda-developers.com/showthread.php?t=466174
I DID NOT DO ANYTHING TO CONTRIBUTE TO THIS. DO NOT THANK ME.
I found the file in this thread and I'm just sharing the love.
Thanks to these people at XDA-Developers
Credit goes to hskoon for posting the original steps, chavonbravo for posting the RC29 file, and JesusFreke for the modified RC30.
Again I did nothing to contribute other than link to the files for you. I do not want to take credit for the accomplishments of those people.
The only part of this that I have done is installing JF RC30 1.3. I've had a rooted G1 for a while now, but now hopefully, now you guys can too!
EDIT: ACCORDING TO THE XDA-DEVELOPERS THREAD IT WORKS 100%!!!