M33 team has done it again. The PSP Slim can now run M33's 3.60 custom firmware. The new firmware has "all the features of 3.52 M33, except the 1.50 kernel support". This means that some homebrew that was developed specifically for 1.50 (e.g. homebrew games that would go into the GAME150 folder) will not work with the custom firmware.
The installation is complex, requiring a Pandora Battery and Pandora memory stick, a non-Slim PSP with firmware 1.50 or custom firmware that supports 1.50 kernel, and of course, a PSP-2000. As always, this is not for the faint of heart nor anyone who hates carefully reading and following instructions, as there is always a possibility of bricking your brand new PSP-2000. As such, use at your own risk. Full instructions for the installation can be found here.
Download M33's custom 3.60 firmware here (scroll down to the bottom of the first post).
[via DCEmu, thanks everyone who sent this in!]