In case anyone was wondering about the effectiveness of right to work laws in suppressing unionization, here is a chart of Union coverage rate by State (the percentage of all employees that are covered by a collective agreement) as of 2010. Right to work states have an asterisk, and are outlined with a black dotted line. (Chart updated, original scale was wrong).
Source: US Bureau of Labor Statistics
Update: This shows, of course, only correlation, and not necessarily a causal relationship. Most right-to-work laws in the U.S. were passed in the 1940′s and 1950′s.
In fact, only 4 states have passed a right-to-work law since 1975.
Right-to-work legislation was used in the American south to prevent unions from gaining strength. Apparently Indiana was different: Prospect: Where Indiana Goes So Goes the Nation.