Beware that half the time the shopback button disconnects itself when you go to the payment page and therefore it does not recognise that your purchase should be attributed to shopback. I have had to fill in 5 missing cashback forms in the last 3 weeks, and need to do 2 more when the waiting period is over.
You shouldn't have to check the connection every time you click a button on the website you are trying to purchase from.