FYI, I own an '07 Forester XS PZEV and have been loosely following these reports. Most of these problems have been traced to the cruise control location. Subaru stuck the cruise control on a stick attached low on the steering wheel itself, and drivers can catch the stick and activate it without meaning to. I've done this myself twice, activating the cruise control and pushing it into "Accelerate" mode with my leg as I made a right turn. It's not pleasant, but ultimately it's driver error...it's caused by either sitting too close to the wheel so your knees are too high, or by having the steering wheel height set too low for your legs. Both times it's happened to me, it's occurred when I've packed my 6'1" self into the car after my 5'5" wife has driven it, and was in too much of a hurry to readjust the seat.
The other cause is the AC compressor. The automatic climate control system runs the A/C compressor almost constantly in the car, even when the heater is on, in order to dehumidify the car interior. If the compressor kicks on and the RPM's are low, the computer compensates for the extra load by increasing the throttle slightly. As the Subaru mechanic told me, this was by design. The problem is, if the computer applies the throttle just as the transmission shifts, the car will experience about a half-second of unplanned acceleration. It can surprise people, but its typically over before you can even react to it.
Nearly all "sudden acceleration" issues have been traced to the first problem though. Bump and a push from a misplaced knee are all it takes. If you're wearing loose slacks, it's even possible to snag the stick and HOLD it in the accelerate position without realizing it. It was an incredibly stupid design, and I've never understood why Subaru didn't just put the cruise control buttons on the steering wheel itself, or put the stick on the steering column, like every OTHER manufacturer does. Oh wait, they did...on the new model Foresters after 2008.
ON EDIT:
A shot of the wheel in question. You can see the cruise control stick in the lower right behind the wheel. What isn't obvious is that the stick is attached to the wheel itself and spins with it as you turn. When the wheel is turned just right to put the stick in the 6 oclock position, it's easily low enough to catch a leg. A quick tap on the end activates the cruise control, and an upward press causes the vehicle to accelerate. I realize that you are familiar with the stick as a former Forester owner, but I thought I'd toss this in just in case my description left anyone else puzzled.