The problem I have with the term "shutter lag" is that it often isn't just about a delay caused by the shutter mechanism itself. The live-view image has to be read off the sensor, processed in-camera, then processed into a JPEG that can be viewed on the LCD/EVF. This takes milliseconds of time, such that the electronic view is time-delayed.
You can see the time delay first hand. Just position the camera in front of you, LCD turned on, such that you can see both the LCD and the subject. When motion happens, you can plainly see that the view in the LCD is delayed; this delay is measurable. It may not mean much for stationary subjects, but try shooting a child's birthday party, for instance, with kids running around, and you trying to capture their fleeting portraits on the fly. Quite a challenge, really.
There are also other delays in these cameras that are sometimes attributed to "shutter lag", like when shooting in full auto and the red eye reduction does its little routine. Or when autofocus can't lock onto a low-contrast subject, and just hunts and hunts. This last cause is less of a problem in u4/3, because the focusing is so good, but anyone coming from P&S cameras knows the routine well.
We can eliminate many of these causes of "shutter lag", except one, the delay in the EVF/LCD; this can only be compensated for by an optical viewfinder.
~Joe