http://www.pbs.org/wgbh/pages/frontline/shows/walmart/
Frontline did an entire episode on Wal-Mart which was quite enlightening. It's available to watch online for free through the above link.
I'm not going to say I'd never shop at Wal-Mart. I do it occasionally. But there are certainly issues with how they run their business - enough that I'll consider shopping elsewhere before Wal-Mart.