The original mechanical shutter gives you a or minimum shutter speed of 1/4000second. This is not that fast, compared to the average dSLR, where 1/8000 second seems to be the standard. Another 'problem' is that you can't use fast lenses (f/1.2, f1/4) in (bright) daylight, without the use of ND-filters.
The new firmware version adds the option of using an electronic shutter to the camera. This expands the minimal shutter speed to 1/32000 and removes basically all problems mentioned before.
This is true up to some extend. It also introduces a new 'feature' when photographing (fast) moving objects across the sensor.
Fast moving objects may be deformed while they are captured. This happens because the sensor is being read line by line from top to bottom, and is called rolling-shutter. So if the capture process has finished reading a line of pixels and moves on to the next, the image has changed little, since the object has moved slightly to the left or right.
Just add a lot of lines and a very fast moving object to the equation, and you end up with deformed objects.
Just compare the photos below. Two of them are shot with the electronic shutter. The other two with the mechanical shutter.
So remember to use the mechanical shutter when shooting fast moving objects. And if it's too bright, get an ND-filter, or buy a dSLR which has a 1/8000 second shutter option.