I found the below story from MLS Soccer pretty informative. The main thrust of the story is the relationship between possession and goal scoring and how not all teams are equal in how effective they are at turning possession into goal scoring. During 2011 the Timbers were near the bottom in the statistic of possession per goal scored. With the additions of Boyd and Songo'o, drastic improvement from Nagbe, and improvement from Kalif and Alexander, I expect this statistic to improve in 2012.

http://www.mlssoccer.com/news/article/2012/04/03/central-winger-why-possession-stats-are-misleading