Failure to think like a physicist
It looks like my attempt to think like a physicist in the Coursera class on Quantum Mechanics and Quantum Computation failed. I tried it again on another assignment and it didn't work, so it's back to the direct approach of attacking quantum mechanics directly by wrestling with the math instead of trying to find ways to avoid work by thinking like a physicist.
But in any event, I still can't recommend this particular class enough. It's an excellent introduction to quantum mechanics and quantum computing, which is something that people in information security should probably know at least a little about. If engineers can one day build large-scale quantum computers, it will make lots of public-key technologies totally useless.
If that's something that might worry you, you should probably understand the technology well enough to understand what it could potentially do and exactly how likely it is to happen, and this Coursera class seems to be a good way to gain that particular understanding.
And the price (free) is certainly right.