I saw this on the front page of Reddit (a news site):
"Researchers have found that low self-esteem and materialism are not just a correlation, but also a causal relationship where low self esteem increases materialism, and materialism can also create low self-esteem. The also found that as self esteem increases, materialism decreases."
Link to whole article on The Daily Galaxy
We've all seen those world survey studies where it turns out that GDP don't always correlate to happiness (BBC example here) but this is the first study I've seen that takes a specific example (materialism) and links to people being less happy.
It also raises the long-term VS short-term argument, which is an important reason why if all this stuff makes us sadder, why we do it at all.