Some stats for you:
Six NL LFs played 1000 innings in their position: Ryan Braun, Chris Coghlan, Raul Ibanez, Garret Anderson, Alfonso Soriano, and Carlos Lee. Let's compare, shall we? (Note: this is organized from ascending innings played).
First, some definitions:
PO = Putouts
Ass = (heh) Assists
TE = Throwing Errors
FE = Fielding Errors
Fld% = Fielding Percentage
DPS = Double Plays Started
BIZ = Balls in Zone
RZR = Revised Zone Rating, the proportion of balls hit into a fielder's zone that he successfully converted into an out
OOZ = Number of plays made outside of a fielder's zone
Now, you can make a strong case that, if you're going to have a defensive liability in left field, it might as well be at Minute Maid Park, where you can throw the ball from home plate to the Crawford Boxes. So there are some major park factors at work here. But Lee wasn't last in any of these categories, except for one that really does matter, RZR. But even in that case, he was only slightly worse than Alfonso Soriano (speaking of oppressive, soul-crushing contracts...) Lee's nine outfield assists tied him with Ibanez for the NL lead among left fielders (again, possibly because of how short LF is at MMP).
Lee also made 51 outs outside of his zone, which is second only to Braun in the NL, though it ties him with Nyjer Morgan, who played in less than half the number of innings Lee played. So is Lee's defense bad? Well, he's slow, and he's a chub. But so am I. But it will take me approximately 2,439,024 years to make $100 million*. So yes, his fielding is bad. But he's only barely worse than another LF in the NL Central with a huge, unmoveable contract.
* - This is something I really regret figuring out. Now I'm depressed.
Wanna take a shot? Take it, then.