Mine are all bent. I think it came from me being really tense when I first started knitting. I noticed that right where I hold my needles over time they would start to bend just a little. So I think it came from constant pressure from being so tense. I don't think that I am quite that tense anymore so I think its better now. But it definately happened.
OTN: Jeckyl and Hyde Hat, Shetland Shortwrap( )
FO: Lacey Stole, Library Capelet, Dead Fish Hat, Tree Bark Scarf
Tension in your hands and the weight of the fabric will bend very thin aluminum needles, but not affect thicker sizes (US 4 and above), as long as they are solid and not hollow (there have been a few of those manufactured over the years). This is especially true of the longer straight needles. The heat of your hands won't affect it-- try passing a needle through a flame: it won't bend in the heat alone. If you have thicker needles and are still bending them, then you must be pressing on them, somewhere, some how.
Combine 5 children running around a living room (playing that game where you try not to touch the floor), dpns on the back of a couch - and yes, you can definitely bend your aluminum needles quite a bit! Beyond that, the only needles I've bent are bamboo needles.