Update: It's now been reported that the JAP version of Lumines does not work with the exploit, so those interested should seek out a USA/EUR version for the time being. Also, the exploit doesn't seem to work properly if your PSP is set to non-English settings. It's likely something to do with unicode when displaying the profile name, but if you are having problems (especially with the EUR Lumines) then try switching your PSP to 'English' settings and enjoy.
Today the Illuminati Exploit For PSP 3.10-3.50 is available, which includes a "Hello World" for PSP Firmware up to v3.50 that opens the door to homebrew, a v3.50 downgrader, and more! To quote from the ReadMe file: PSP Files: Random Topmenu PRX Mod v2 For Custom XMB For PSP, Hybrid Firmware 3.00 IE-A Update 1 For PSP, and PSP-PDA v1.3.1 For PSP.