I was in my local H&M yesterday. Daughter bought a top and a hat and was given a £5 giftcard, valid from 16.810 to 29.8.10.
I asked about it and was told that with every purchase in the children's department they are giving away a giftcard. There is no minimum spend to get the giftcard and no minimum spend to use the £5, just use it during the two weeks specified.
Offer finishes tomorrow, I believe, the day before the giftcard becomes valid.
We went back and bought another hat for £2.99 and were given another £5 giftcard.