CELL phones: I heard the jury is still out on adverse side effects, some studies in Europe showed more benign tumors in heavy long-time users.
I don't let the kids use them, maybe when they're adult-sized. I'm sure there's some small adverse side-effect to my use. I wish the phone cos would give you the option of having a safer, more shielded phone, BUT, that would require admitting a problem in the first place, which they would never do.
As a technology alone, though, it's awesome, has revolutionized the world.