I'd say almost definitely Accelerator Position Sensor failure. I had this happen last January.
The OBD II code is P1120
I would advise against driving the vehicle as much as possible, because of the dangers posed by the thing failing in the middle of the road as you said. That's how mine first went out, and I almost got hit because I couldn't accelerate out of the way of another car. Shudder to think what would happen if it failed on the freeway.
I would also advise on being prepared to be without the vehicle for about a week. As you can see on the paperwork I've scanned in below (emitting my identifying data for obvious reasons), I took it in with the problem the morning of the 14th, and got it back on the 19th.
It's not cheap either - the cost of the part is $300.33 with labor of $195.88 = 496.21 + 24.78tax = $520.99
Merry Christmas..... sry
http://i72.photobucket.com/albums/i190/kalimando/AccelSensorServiceWrite-up.jpg
http://i72.photobucket.com/albums/i190/kalimando/AccelSensorInvoice.jpg