Ive had overdraft off on my account since i opened it. However theres been a few things that still are allowed. My truck note is one of them, and state/federal/irs stuff im told would likely be allowed too. I once double paid my truck not on accident, and that was a fun trip to the bank to put a stop payment in.

IIRC part of the problem is that merchants don't necessarily post charges to your account immediately. They place a hold on funds, but it's not necessarily charged. That's especially true for buying gas, where the amount you are going to spend isn't known until after you're done filling your tank. The way around that is to have to pre-pay for gas.