Instant Cashback for some

Microsoft's Live Cashback offer just got alot better. At random people have been getting instant cashback. Just today I purchased a $499.99 Asus EEE 1002ha from Ebay and received an instant $150 back to my paypal account. Normally you have to wait 60 days to clear Cashback payment. So far no one knows the formula MS is using to decide what gives you instant Cashback savings.