It looks like the PSP firmware is hacked at the same rate as it is being upgraded. A developer known as hitchhikr of "hitchhikr SoftWorks" and the Neural group have come up with a Proof of Concept of a 2.50/2.60 Firmware Exploit.
The exploit takes advantage of an added security check in 2.50/2.60 Firmware for sceKernelLoadExec, which is responsible for loading EBOOTs. Somehow, Sony also accidentally added an overflow bug, which means this exploit will not work with 2.0 and 2.01 Firmware.
Once implemented and tuned for "normal users", this will bring 2.50 and 2.60 Firmware up to the same homebrew capability as that for 1.50, with full kernel mode access. As it was the case with eLoader, Grand Theft Auto: Liberty City Stories will still be required.
Fanjita, the developer of eLoader, is already working with hitchhikr on incorporating this new exploit into an easily executable means by eLoader means. Fanjita promised that a generic application for developers will be available in a short time. However, something usable for non-devs will require much more time to finish.