This this this this this http://blogs.reuters.com/felix-salmon/2013/01/14/the-invidious-reach-of-personal-finance-snake-oil/
Thanks Logan! But actually I'm kind of a jerk.
Matt Yglesias has a good post on this. Basically U-3 tries to measure the thing that is "people who want jobs but don't have them." Everything else doesn't try to measure that. Maybe those things actually measure it better than U-3 but, since they don't try to, that would be pretty coincidental and hard to extrapolate trends from.
@stuffisthings Thanks! Also, please do click through from RSS occasionally. That way we get money. Money.