Greg, admin from PSP-Hacks.com, has managed to downgrade (using Downgrade) his very own PS3 from firmware v3.50 to 3.41 but when attempting to reproduce the downgrade on the same PS3, it semi-bricked (aka semi-dead). The good news is that Greg eventually figured out how to fix it. And so can you, if you ever semi-brick your PS3.
Use PS Downgrade with extreme caution. I’ve semi-bricked my PS3 while playing around. As PS Jailbreak stated, I guess you can only attempt a downgrade once. Now I don’t believe my PS3 to be fully bricked; I say semi because I can repeat step 6 and the system does try flashing PS3UPDAT.PUP from the USB key again. During that flashing process it succeeds throughout many stages; however, towards the end it fails with:
Updating or Verifying failure 0x8002f057
UpMng.UpdatePackage() failure
manufacturing updating FAILURE(0x8002f057)
Total Elapsed time = 156974 msec