Ever wished you could go back to firmware 6.20 after updating to firmware 6.38? Now you can, thanks to homebrew dev some1's 6.38 Downgrader. The homebrew app, based on Davee's FW 6.35/6.31 downgrader allows users to downgrade from firmware 6.38 to 6.20.

Developer's note:

This a very simple app, just put the official 6.20 updater in (ms0/ef0 accordingly)PSP/GAME/UPDATE, and run the downgrader, this will reboot into the 6.20 "update", and allow you to downgrader to 6.20. Has been tested on 1k, 2k, 3k, and Go (added support for 07g/09g).

I will be releasing the source on May 29th.

Instructions:
If you have anything lower than an 07g place the 6.20 update in PSP/GAME/UPDATE.
If you have an 07g or an 09g, place the 6.35 update in PSP/GAME/UPDATE. 

Important note: You run the application at your OWN risk. I am not held accountable if you fuck up your PSP.
Another important note: After you downgrade to 6.20, you will get a BSOD (saying that your system information is corrupted), this is OK, just click circle to reset your system information and you will be back to normal.

Final important note: It does indeed still support 6.35/6.31