http://insider.espn.go.com/insider/insider/news/story?id=4946751

The Whole Argument is summed up nicely here-

"Some insiders like the stat because it accounts for factors -- quality D, effective screens -- that don't show up in box scores. Others, like Nuggets stats guru Dean Oliver, say, "It's noisy, uncertain and kind of a black box -- you have a hard time understanding why it's coming out the way it is."

The stat is also much better at assessing a player's value to a particular team than comparing him across teams. For example, it can reveal Wade's value to the Heat, but not whether he'd be more valuable than LeBron James is to the Cavs. It also doesn't factor in substitution patterns. The Thunder's Jeff Green has a league-worst minus-13.6 rating, which doesn't take into account that he's often the lone starter running with four bench players and he's logged twice as many minutes without Kevin Durant or Russell Westbrook as last season, when his rating was minus-3.51."

A few tidbits

Jonny Flynn, Ryan Hollins, Al Jefferson, Corey Brewer, and Ryan Gomes make up by far the worst 5 man unit in the entire league at -21.70 per 48 minutes.  The next worse group is Brook Lopez, Chris Douglas-Roberts, Courtney Lee, Devin Harris, and Yi at -13.85 per 48 minutes.

The three players who benefit their team from being on the floor: D.Wade, Anderson Varejao, and Kobe Bryant