Sony plans to make PSP game Resistance: Retribution and PS3 game Resistance 2 work together in a couple of ways.
The first unlocks extra gameplay via Infected mode: an alternate story for Resistance: Retribution where Grayson becomes a Specter and suffers from weird strain of the Chimeran virus, according to the US PlayStation blog.
The benefits to this are regenerative health and the ability to breathe underwater. Plus, Specter Grayson gets a Resistance 2 gun to use, and can unlock Plasma Grenades for that game by gathering all the available intel.
To use the mode, simply connect the PSP to the PS3 using a USB cable, then head into the Resistance 2 options and select "Infect my PSP!"
The second fancy feature is PSP Plus, which lets Resistance: Retribution be controlled by the wireless DualShock 3, rather than the fiddly PSP nubbin. As this makes things a little easier (and rumblier), developer Sony Bend is taking away aim assist and upping the challenge in PSP Plus mode.
Resistance 2 is due out for PS3 in November. Resistance: Retribution will head to PSP next spring.