Hi Gherkin:
I would check to see if you computer is being grounded properly.
If you are using the small adapter which attaches to you power adapter, it only has 2 pins and will not be grounded.
If you are using the cable which attaches to you power adapter, it has 3 pins and should be grounded.
Ensure that you receptacle is grounded.
Also I have read some information where someone was having a similar problem and examined his power adapter and found that where the cable from wall attaches to the power adapter, the ground terminal in the power adapter was covered with plastic. I guess it was supposed to be removed before using, but it was preventing the power adapter from being grounded. Once he removed the plastic, it was fine.
I also found the following links which may be interesting. http://upsticksandgo.com/getting-buzz-macbook-pro-electric-shock-travellers-tip/
http://apple.stackexchange.com/questions/17575/how-to-properly-ground-a-macbook- pro