Sony pushed out PSP firmware 6.38 just a bit ago and guess what! You can still run signed homebrew! Of course, no one know if using the downgrader will work from this new firmware or if the recently-released custom firmwares will install from this firmware, so take caution! All Sony says that they released in this update was a “Security patch to add stability.”
Of course, that’s code for, “We’re trying to combat homebrew!”
To download and install this firmware on your PSP, you just need to go to Network Update on your PSP’s XMB and install it from there.