iBook electrical shock

[Samantha Packingham]

I noticed today, that when working with my iBook (dual USB) on my lap, 
it is shocking me when it is plugged in.

This may have been going on for some time, I live in Michigan, and it 
is just getting warm enough to wear shorts.

The shocks are coming from the four metal discs at the corners.  It 
goes away when I unplug the power source...but it just doesn't seem 
right.

Has anyone experienced this?

Any ideas?

Thanks!

Samantha