First, a lot of people have been complaining about... Well asking about if you can do a software downgrade on the firmwares 3.51+ and what Sony did was put a detecter in the 3.51+ firmwares. So, what I've been telling everyone who's asked, there WILL NEVER BE A DOWNGRADER FOR 3.51+!!!!! Use the damn pandora battery. Plese SEARCH for a pandora battery creater tutorial. Also he only way that PSP-3000 Owners can downgrade is if you do a GripShift exploit. (Available on Youtube) Anyone lower just search depending on your PSP either search "PSP Phat pandora tutorial" or "PSP 2000 Pandora tutorial". Chow
I am not sure where you are getting your information from, but the reason there is no downgrader for 3.51+ firmwares is NOT because $ony put 'detectors' in the firmware-that is utter nonsense. The release of the pandora battery took care of that-and so it was deemed redundant (much like this thread) to explore other means of downgrading when the pandora battery/MMS could easily do it without the need for a game exploit, hack, etc..
Also the PSP-3000 cannot be fully 'downgraded' at this time-
Yes, there is the exploit-however, that does not enable your psp to play games from the memory stick, nor does it allow you to run emulators and other homebrew as you would on the PSP-1000/2000 as there are too many variables involved. Most of which have been patched by $ony already in the 5.03 update.
While I applaud your effort, it would be wise that in the future you would take the time to do a little research before just posting your two cents and then labeling it as a 'guide'. People are going to ask the same questions over and over again regardless. If you want to be helpful, why not respond to those threads and direct people that need help to the right place rather than just posting a rant with useless information?