That's interesting. How do you "fund" the card? Do they apply a preset limit based on your Coinbase account? If they do how is the tracking for how much you've already spent accomplished? Is there a number or website you can use to see how much is left on the card? Surly you aren't saying the card is limitless?
There is a website and a mobile app. Here's a screenshot of my account, showing my pending purchases for the day:
They appear to be keeping a register of pending transactions on their side. Prior to transaction approval at point of sale, they take your wallet balance, convert it to USD, then subtract pending transactions. If the result is more than your purchase, they approve it.
The daily limit is $500, but that's clearly communicated as a limitation of the Beta program. The limit once it hits public release hasn't been defined.