That is the sound of one box cracking. The Saturn Expedition Committee reports a successful writing, compiling and
executing of the first homebrew code on the
PSP, compiled with the ps2dev chain. They've
released the app for download, though as noted it will
only run on PSP 1.0 firmware (American PSPs shipped with version 1.5) for now.
Hello World PSP download
[Thanks, Greg and Mike]