I was curious earlier about how long the actual shutter lag on the iPhone 4 camera was. So I did a quick test. I used this website to run a stop watch and then released* the shutter when I given second rolled over.

http://www.online-stopwatch.com/

The result was a little surprising, the shutter lag appears to be just a tiny bit less than zero seconds

Either I am anticipating the roll over (which what I am seeing suggests is not true, but then the whole brain vision system can be tricky) or the iPhone is actually taking the picture the whole time you have your finger on the button and saves the image that was there just before you released the shutter.

Even if I stab at the button as it rolls over the apparent lag is less than a couple of hundred milliseconds.

* I rarely press and release the shutter in one movement on the iPhone, you get much better results by pressing the shutter and then sliding your finger off it