One passage from a Baseball Prospectus article (subscription) about park factors:
Additionally–and this is a more vital failing of runs-based park factors–they don’t tell us how a park accommodates left-handed batters and right-handed batters. For instance, Comerica, Wrigley, Safeco, Fenway, Shea and many others affect hitters quite differently according to their handedness. To cite one extreme example, from 2002-2004, Minute Maid Park’s average home run factor for right-handed batters is 116, while its home run factor for lefty hitters is 84.
Thus, Dunn’s homers might actually be depressed by heading to the supposedly-hitter-friendly Always Enron to Me Ballpark. So don’t try to get him, Houston.