A blog called Psychotherapy Brown Bag has done a good job of reviewing a recent paper which continues to add to the pile of evidence on the centrality of experiential avoidance in maintaining a variety of psychological disorders. This paper is about the Trichotillomania and is worth a read. Here's what they had to say about it:

In a study just released in Behaviour Research and Therapy, Anna Shusterman, Lauren Feld, Lee Baer, and Nancy Keuthen (2009) utilized data from a massive online survey to examine the role that emotions play in prompting and sustaining this disorder.  The description of TTM in the DSM-IV-TR as well as a number of prior studies have linked TTM behaviors with a sense of relief on the part of the individual exhibiting the behavior.  In other words, many individuals have reported that pulling out their own hair has resulted in immediate decreases in negative emotions.  Despite this potentially valuable function, the behavior also includes a variety of less comfortable correlates, namely subsequent feelings of shame and guilt and a strong desire to cease the behavior.  So, the behavior becomes rewarding through its ability to quickly reduce certain negative emotions, but also results in several emotional and social consequences.