My response would be:
"Wow, that's awesome, this devil must be a stand up guy."
This means he's cured multiple diseases, made the blind see, given amputees new limbs, lengthened the lives of many people, saved lives, given us hygiene so that we don't fall ill with things like cholera, he has saved numerous born infants and reduced death during child birth, he has been responsible for avoid crop failures so that millions (heck billions) can eat, he has been responsible for all the technology that improve our lives, from computers, to aeroplanes to GPS and heck, the devil even got us on the moon, it is the devil who is responsible for the networks that connects friends and family around the world and brings people from all walks of life together, the devil is also responsible for the technology where Christians can post their blogs and proselytise via new mediums (but I hear he's sorry about that one) and there's a lot more he's also responsible for.
Damn, this devil bloke seems to really take a caring and active interest in the progression and potential of the human race. Well, it's no surprise really, I mean, look at the Adam and Eve story, God required their ignorance and rewarded their obedience, whereas the devil offered the gift of curiosity, of learning, of knowledge through the temptation of Eve to get her to eat from the tree of knowledge. According to the bible the first scientist was a woman. Of course, God punished them for wanting to know more for wanting to learn more about the real world. So I think it's very plausible to suggest science is the work of the devil, because all scientists are doing is what Eve did in Genesis, feed from the tree of knowledge. God doesn't want humans to be knowledgeable, he wants them to be ignorant and bow down to him in worship. Regardless of the suffering caused by their ignorance.
I think this all puts the devil in a more positive light. After all, who's the biggest causer of pain and suffering in the bible? Not the devil. Who's the biggest murder in the bible? Not the devil. Who's merciless and vengeful when it comes to defiance in the bible? Not the devil. The devil wants man to turn against God and if we're to understand the bible to be factual, particularly the old testament, then God is the biggest tyrant of them all. You can probably think of the devil to be like Marduk in Mesopotamian religion, who led an army against the tyrannical creator, Tiamat and was the one to slay her.