From Boing Boing:
We know that the general anesthetics we use today are safe. But we know that because they’ve proven themselves to be safe, not because we understand the mechanisms behind how they work. The truth is, at that level, anesthetics are a big, fat question mark. And that leaves room for a lot of unknowns. What if, in the long term, our anesthetics aren’t as safe for everyone as we think they are?
What makes anesthesia fascinating, and quite different from other medical aides, is that it literally makes modern surgery and medical technique possible. Everything from dental  to cardiac  surgery requires anesthesia of some sort. Medical procedures also require a steady hand and a steady body; keeping the patient still is of the utmost importance.
The need for anesthesia occurs every day. Necessarily, we are dependent on its effects. This immediate need to be put under is such that we are able to take more of a risk than we might with a new drug or procedure. It appears to be safe in the short term, so we give a little by becoming blind to the long term.
A hat tip to Marginal Revolution for the pointer.