I've just received some tiny (6mm diameter x 0.5mm thickness) magnets I ordered on ebay yesterday. After trying with the PW and the Oberon cover from my K3, it works fine for the wake/sleep thing when put in the small inner pocket - so far so good - but I've also tried just putting it on the outside of the front of the cover and it does works through the whole 5mm of leather

so I will have to put an extra layer of something or other to prevent that, otherwise I won't be too happy, or I might just get even smaller magnets (seen some 3mm x0.5mm)
Oh and the magnets were £2 something inc p&p for a pack of 50... So got spares a plenty

will keep some to make stuff for the magnetic board in my study but if anyone in the UK wants some, just PM me your address and I'll send a few