[Andrew Stephens]

Should it do this?

Just unplugged magsafe from mac. OK wrong way round as power still plugged in other end. Accidentally touched mag safe end and received a great belt from it. Finger still tingling 5 mins later?
Should it do that?

[mduell]

Just like every other laptop power adapter on the planet, you can unplug it from the laptop without unplugging it from the wall.

There should only be about 20V across the leads, so it wouldn't shock you that bad. Could have been a static buildup issue.

[ghporter]

--or the fact that the power block was only connected with a two-prong plug. No ground means there's no telling what sort of voltage is on the shell of the connector.

And note that mduell is 100% correct about disconnecting the connector from the computer first-this is even the way Apple instructs you to do it. The connector includes sense pins that basically turn the adapter on or off as appropriate. We're not talking about a dumb transformer here, this adapter is very smart.

[Andrew Stephens]

Adapter was plugged in via the extension lead with the earthed plug, not the duckbill part. Must have been static from my daily trips across the office carpet tiles.

[ghporter]

Or the outlet isn't properly earthed. This happens sometimes. If you'd been shuffling across the carpet, then touched the shell of the connector, you could have gotten a shock from your body's static buildup. But if you were just walking normally, it's not terribly likely that this is what happened. From your language I believe you're somewhere in the UK or surrounds. It's typically way too humid, even in an office, to have that sort of static build up. I think you should report that you got a shock from the earth terminal of your power adapter to your building maintenance people; it wouldn't hurt for them to make sure the outlet is wired properly.