A few years back I had the good fortune of owning a WRX wagon whose tenure began with me leaving it unmodified for as long as I could stand. All told, it only took about two months for all rational thought to be overwhelmed by the relentless pursuit of ponies and I found myself at a highly regarded, local tuner.
After several conversations with the owner, I was informed that the ECU of the Subie was highly adaptive and had the ability to learn a few tricks from its driver. In the end, a quick reflash of the ECU's fuel and ignition maps could bring a few more ponies to the party. All it took was a laptop and a couple dyno pulls, and I was ten HP richer.
It seems that Toyota has a similarly adaptable ECU in its Camry, which takes cues from the driver's inputs and then operates the engine accordingly. If the driver is say, timid and easy on the throttle (not going to make generalizations about Camry drivers here) then the ECU will recognize the driver's overall character and taper back on the heavy dumping of fuel and air into the cylinders.
The problem it seems, is that when said timid driver needs a boost of juice, the Camry's brain doesn't cooperate, causing driver's to complain of mild bucking and hesitation. The drive-by-wire throttle (we still like our cables, thank you) is partly to blame, as it sends the majority of information back to the ECU.
Toyota released a TSB for the issue and a quick software tweak seems to solve the problem. Only owners that recognize a hesitation in acceleration are encouraged to come in for the service, though it's safe to assume that most Camry drivers won't notice a problem.
[Source: Automotive News]