I'm actually a big fan of using the Bible in conjunction with the Qur'an in my studies. People (meaning Muslims) tend to say "Oh, it's a corrupted book" and dismiss it, but I think the Bible has a lot of wisdom to share with us. Provided that we study the Qur'an alongside it, I don't see how using both can be wrong.
If we weren't meant to use the two together, why would the Qur'an have been sent as the corrected book? Why were we told to ask the Christians and Jews (those who had the book before us) if we were in doubt about what was revealed (the Qur'an), if the Bible was so utterly unreliable? I think Muslims do themselves a great disservice by not studying the Bible.
It's because they refuse to study the Bible (unless it's to find proof of how Jesus isn't God according to the Bible) that they feel the need to resort to the manmade, truly corrupted books of hadith.
The hadith, quite frankly, make me angry. They ensure that Muslims are seen all over the world as backward, primitive, tribal people who see women as property and merely the outlets for mens' sexual urges. They're why people think Muhammad married and had sex with a child and why they think he murdered or ordered the murders of those who opposed him. They're why so many Muslims take pagan superstitions (against black dogs, photos of living things, etc) as religious edict instead of the cultural baggage that they really are.
Even lifelong Muslims can't see the Qur'an for the hadith, because their perceptions have been warped and dictated by scholars their entire lives. They've been brainwashed to think that Allah isn't enough, that the Qur'an Alone isn't enough, that you can't think for yourself in matters of religion because you "aren't a scholar" and "don't have the right education" for it, and that we need more than that to believe, live, and die as Muslims.
And so they conclude that you can't be a Muslim without the hadith. That Islam is incomplete without the hadith, despite the fact that Allah explicitly stated several times in the Qur'an that it was complete, detailed, and the guidance for Muslims.
People don't really trust in Allah's mercy and forgiveness, and because we don't have "Jesus-as-God", they feel they have to make up false "get out of jail free" cards like "fasting on the day of Arafat erases your sins for a year back and a year forward". Because of that lack of trust, people feel such fake "reassurances" are necessary. But when you truly trust in the goodness and mercy of Allah, you're willing to take Him at His word and don't try to make up such crutches.