yep, mine has it too, one corner where my wrist rests onto the casing is kinda worn off and the metal casing comes in direct contact with my skin...
due to magnetic induction from the magnets inside (how the f do they work ?!) static charges build up sometimes and give me a tiny shock :)
generally its only when my laptop isnt earthed (only the 4 rubber foots touch the table, nothing else) and i haven't touched it in a while (so static had a chance to build up...
its sufficient to touch the casing with a finger first to discharge it, otherwise if it discharges through your wrists it feels much harder :)
once its been discharged and i keep working on it it generally doesn't happen again ....