I was reading a Newsweek article about how stress early in your development helps you cope with things later in life, and how you can cause your brain to develop in ways that are resilient to stress. It fortunately/unfortunately included some details about what stress does to your brain.
Since I am prone to unnecessary stress, my biggest take-away from this otherwise optimistic article was OMG, prolonged periods of stress causes your medial prefrontal cortex to shrink*. The medial prefrontal cortex is associated with self-referential activity and has high levels of activity when you are not actively thinking; the prefrontal cortex is associated with "executive decisions" of good vs. bad. In conclusion, being stressed out makes you less creative and will probably ruin your career, so you should probably stress about that. ;)
* It can grow back if you are not under constant stress.