1/4000 v 1/2000 shutter speed - help

Hi,

There doesn't seem to be very many differences between the E-PL1 and the E-PL2 except the PL2 has a higher shutter speed (1/4000) and some red dots (lol)

It'd be great if someone can explain the importance of shutter speed and how much of a difference 1/4000 'v' 1/2000 makes???

Thanks

L