92w ago - Today Italian site
DiGiTaLAnGeL (linked above) reports that they have successfully downgraded a PS3 Slim 3.70 Firmware unit to 3.55 Kmeaw Custom Firmware, followed by a
New Method - PS3 Downgrade v2 Supports all NOR Flash from
TwoStone.
Similar to the
PS3 Firmware 3.6x Downgrade via Infectus, this round they have downgraded a PlayStation 3 v3.70 Firmware console using
ProgSkeet with the assistance of
Dospiedra with a roughly translated
PS3 3.7x Downgrade for Slims and Fats with NOR Flash now available.
To quote, roughly translated: The first downgrade to 3.70 on PS3 Slim 3:55, DiGiTaLAnGeL tested by us!
For the first time, we have been involved in something truly spectacular
We were the first in the world to test the downgrade from 3.70 to 3:55 on a PS3 Slim (With flash memory, "NOR") using the ProgSkeet and patched some files provided by dospiedra, a famous Spanish coder already riding high for having discovered the method of going back to 3.55/3.41 with the PS3 (FAT flash memory "NAND").
After several attempts, in collaboration with dospiedra, we got to go back from 3.70 to 3:55, enter the factory mode with a simple key to jailbreak, rifleshare a modified version of 3:55 to prevent the SYSCON (the registry in between downgrades) was consulted during the downgrade and now we are happily at 3:55 KMEAW!
With this version of moddata 3:55, you can perform a memory dump today and you can switch on the fly from 3:55 to 3.70 without having to do this all the time-consuming process: using progskeet fact you can go straight to 3.70 changed to 3:55!
Dospiedra said it will release details on the patches applied to the NOR and the update file as soon as possible.
New life for those who arrived too late to enjoy the benefits of the 3:55?
and now square is dead to me! 
I don't have Progskeet and I don't want to have it btw...
Thanks!!
The other guide doesn't involve the Infectus as it doesn't support NOR flash. You'll need to be looking into buying a progskeet...
This method should also work for CECHH and later FAT models - they have also 16MB NOR-flash. Fatties CECHA..CECHG need another method.
Swapping HD and flashing proper image.bin won't take hours. Cool would be to glue a PCB with 16MB NOR flash and connector to HD so you would swap the proper flash the same time you swap the HD
With this method you can use CFW with it's advantages or swap to 3.70 and go onlline.