Word has come straight from Tokyo that your PSP is going to start rumbling: PSP Plus is a new feature that will be included in upcoming game Resistance: Retribution. You'll be able to control your PSP through a DualShock by plugging you AV-Output capable PSP into your PS3 USB port, and control the game with the larger, more awesome controller.
It disables aim assist in Resistance: Retribution, and lets you change the control layout to take advantage of the PS3 controller's extra inputs. Plus, like we said, it adds the DualShock's rumble!
The option requires that gamers have a copy of Resistance 2 in their PS3s, but will not require a firmware update for either the PSP or PS3.