There's a thread over on the Sun Deck where a poster mentions seeing it written that Adam Dunn is the 5th-best defensive LF in the NL at the moment. No link is provided and it certainly goes against the mass perception of Dunn's defense.
Certainly he's no Carl Crawford out there, but he's better than he was last year. He's not elegant, nor terribly instinctive, but he can cover a decent amount of ground when he gets a bead on a ball and his arm is pretty good for the position (traditionally a weak armed position).
While it might seem outrageous to think of Dunn as potentially one of the better defensive LFs in the NL, I think we forget exactly who the competition is. Here's a breakdown in two categories (solid defenders, bad defenders, the names are listed alphabetically):
Jose Cruz Jr.
These are the players, who've played the most games in LF for each of the 16 teams in the NL. There really isn't a good defender in the bunch. Bonds, Duncan, Lee and Willingham probably deserve to be in their own "super awful" category. If someone was ranking defensive LFs in the NL, it's possible Diaz missed the innings cutoff, so a guy from the "bad" list certainly could have been #5.
The AL has a better set of defensive LFs, but it also has Manny Ramirez, Raul Ibanez and Frank Catalanotto.
My point being that when you look at who is playing the position, Dunn's a fairly standard kind of bad. I know his UZR rating for the year is low, but others are worse and my guess is varying rating systems will show that Dunn is no worse than the standard bad defensive LF, which accounts for the majority of players out there.