DeRosa, who's played for six different organizations since entering the MLB in 1998 (Braves, Cubs, Indians, Cardinals, Giants), has spent the past two seasons with the San Francisco Giants. In 2011, he hit .279 with 12 RBIs and an on base percentage of .351. He has hit 93 home runs over his career.
DeRosa can play all over the diamond. He has spent much of his time at third base, but has experience in the outfield. Since 2009, DeRosa has only committed four errors in the field. In 21 games at left field in 2010, DeRosa was 31-31 in terms of put-outs and had a fielding percentage of 1.00.
DeRosa will be productive where ever the Nationals decide to put him. I would expect him to be spending most of his time in the outfield or second base since the Nationals have Ryan Zimmerman at third and Michael Morse/Adam LaRoche at first base.