Update #2: some1 has released yet another update to his Downgrader making it compatible with the just released firmware 6.39. Download links below have been updated.

Update: some1 has released an updated version of his 6.38 Downgrader to be compatible with 07g & 09g PSP models. The download link has been updated below.

We have been all waiting for something like this!

PSP Developer some1 has today published its PSP OFW 6.38 Downgrader to contribute to the Genesis Competition!

The downgrader works on a original 6.38 FW (HEN or CFW is not needed to downgrade!) and you can downgrade to Firmware 6.35.

It supports all PSP models (1000, 2000, 3000 and PSP Go) except 07g/09g (newer = 3000).
Support for 07G and 09G will be added later by downgrading the PSPs to OFW 6.35 instead of OFW 6.20.
With 07g & 09g support added, 07g & 09g model PSP-3000s will be downgraded to firmware 6.35, while all other models will be downgraded to firmware 6.20. You will need to include the appropriate firmware updater (either 6.35 or 6.20), which you can download here.

If you have a PSP-3000 and do not know which modules your PSP has installed, you can download and run the PSP Module Checker to find out, then proceed downgrading.

Download:http://www.megaupload.com/?d=HHRR8J9D

Source: [You must be registered and logged in to see this link.]