As expected, the PSJailbreak has been reverse engineered and an open source hack, that can be flashed to a cheap USB key, has been released.
The new hack, dubbed PSGroove, can be compiled and flashed to a Teensy++ USB Development Board or AT90 USB Key. The initial release of PSGroove had the ISO booting ability disabled because its developers are interested in enabling homebrew games without encouraging piracy; however, a second version with that functionality enabled has been released soon after.
Both the Teensy++ USB Development Boards and the AT90 USB Keys are out of stock at most retailers due to the unexpected demand. Backorders are expected to be met within 2 weeks. Several hacking groups are working on PSP, iPhone, Android and TI Calculators ports of the hack, so you might be better off waiting for one of those hacks to be release instead of booking a USB development board.