If I use a short shutter speed, I do not notice any difference because the shutter speed is fast enough to freeze any movement caused by mirror vibration.

If I use a long shutter speed, I do not notice any difference because the mirror vibration time is insignificantly short compared to the long amount of time the shutter is actually open.

I do, however, notice image degradation caused by mirror vibration when I mount my camera on a telescope and use a shutter speed between 1/2 second and 1/15th second. Thank goodness my SLR's mirror lock-up feature is very useful for avoiding this degradation.