In the last 30 days, I've received $3.72 in Cash Back Bonus funds from my PayPal debit card. Is it worth it? I think so. That's not a lot back, but keep in mind I haven't used the debit card exclusively. I have also used my bank cards from time to time, and I get nothing back from them.
Learning how much your PayPal debit card is paying you back is fairly simple. Go to your complete history. In the drop-down menu for Search/Show, select your debit card choosing either simple or advanced. They both will give you the amounts of Cash Back Bonuses you've received and you don't have to search through every transaction for the month.
I searched from October 8 to November 7 so I could just see what one month's worth of Cash Back Bonus would be. The more I use my debit card, and select "credit", the more money I'll get back. This tempts me to upload more funds from my bank account so I will use the debit card more.