Hairston got off to a slow start with the Cubs and overall wound up hitting just .172 with a .232 OBP and a .434 slugging percentage. But those numbers don't tell the whole story, as Scott was a victim of one of the craziest BABIPs I've ever seen (.129), which is an indicator that tells us he's been very unlucky. The Nationals don't have a glaring need for Hairston, but Denard Span has struggled a bit against lefties (although he hasn't historically), so maybe Hairston plays center against lefthanders and serves as a fourth outfielder.
Hairston was scheduled to make $2.5 million in 2013 and another $2.5 million in 2014. That means the Cubs save about $1.25M this year and $2.5M next year on Hairston's deal (assuming they don't include cash as part of the package). It's unclear at this time what the return for Hairston is, other than a minor league pitcher, but we'll update this post when we get details.