Critics contend that the constant motion of atoms and molecules makes molecular machines nearly impossible to construct. Heisenberg's uncertainty principle -- the theory that the more you know about a subatomic particle's position, the less you know about its momentum, and vice versa -- also argues against nanobots. How can you manipulate atoms if their component pieces are so hard to find?

I've heard this one before and it's pure bullshit. Don't know how to build one, fine. Van der Walls forces would keep it from locomotion, possibly. Heisenberg uncertainty principle preventing from finding ATOMS? Bullshit, pure and simple. Atoms are only weakly affected by the HUP. Electron, proton and neutron free particles, sure but, not for a system of bound particles like an atom, which is much larger than the fundamental size of it's constituents.