The insidious thing about long-term unemployment is that it builds on itself - the longer you are without a job, the harder it is to get one. The Bureau of Labor Statistics finds that the chance of someone unemployed for less than five weeks finding a job in the next month is about 30 percent. For someone unemployed 27 weeks or more, it's just 10 percent.
This seems like a nonsequitur. It's probably not so much that a longer unemployment spell makes one less employable, as that the less employable suffer longer unemployment spells. That's not to deny that one picks up human capital on the job, but I think an unemployed person would be mistaken to think that these statistics are indicative of how much his employability erodes for each week he's unemployed.