In his latest colum, Ken Rosenthal includes this nugget about Adam Dunn's future in Washington:
Entering the season, we all knew that Adam Dunn could hit. Here is a guy who consistently mashed 40+ home runs every season and produced a yearly OBP somewhere in .375-.380 range. His high strikeout rate leaves something to be desired, but given all the other assets he brings to the table, it's easy to see why Dunn has been one of the most productive power hitters in baseball since 2004.
The major flaw with Dunn (outside of his foot speed, of course) has been his defense. Since 2005, Dunn has statistically been one of the worst defensive players in baseball no matter what position he was playing. According to fangraphs, Dunn's lifetime UZR at 1B is -28.2 and an abysmal -71.5. And no, that's not a misprint. In the National League, there's almost no chance that a contending team could compete with 2004-2009 Adam Dunn playing defense everyday. So it's easy to see why the Nationals have been hesitant to give Dunn a long term deal even though he will be a free agent after the season.
The biggest change in Dunn's game this season has been on the defensive side. Now as the Nationals' everyday first baseman, Dunn's UZR is still not very impressive (-1.3), but given his career UZR at the position, Dunn's play at first base has dramatically improved.
And if your the Nationals, you can live with Dunn's play at first base. Even if Dunn remains a slightly below average first baseman, it will still make him much more valuable that he has been in the past as long his offensive production does not suffer.