has released a new Custom Firmware Plug-In that allows users to save/load savestates of their current progress on PSP titles. Dubbed PSPStates, the plug-in is still in the experimental stage and currently is only compatible with Slim units, due to the increased memory usage.
It is advised to disable any other plug-ins while using PSPStates, as well as backup all data on your memory stick in case of data loss. Additionally, the plug-in is written specifically for 4.01 M33. Savestates created likely will not be interoperable with future Custom Firmware releases.
As a final note, it is highly stressed that you do not use the plug-in with a UMD inserted. Use of the ISO driver March33, which can be selected in the XMB by pressing Select, is recommended.
Download: Experimental PSPStates Plug-In for PSP Slim
Make sure to read the included readme file for detailed installation instructions.