Shareholder activism is having an impact, according to a new report by Governance Metrics International (GMI).

One area seeing significant change is takeover defenses. In 2002, more than half of companies had “poison pills” to thwart potential takeovers; that compares to 16 percent today. As a result, fewer shareholders voted on this issue in 2011 – just one vote, versus five in 2009.

Another area is board declassification. Currently, just one-third of boards are classified. That's the lowest level since GMI has tracked this data. “Boards may feel uncomfortable being too far outside governance norms, so as more companies declassify, pressure increases on the holdouts to follow suit,” the report notes.

Another shift has occurred in the rights of shareholders to call special meetings. Currently, shareholders have no right to call  special meetings at just under half – 49.6 percent – of the companies in the S&P 500. That's an all-time low, GMI says.

One issue that is emerging as an area of concern centers on allowing shareholders to act via written consent. This came up for a vote 32 times in 2011, up from zero in 2009.