SEM provider PM Digital's May 2012 Rewind Index, which measures U.S. paid search performance for online retailers, suggests that while average CPC's dipped in May (following 2-3 percent dips in immediately prior months), much of the declining activity can be attributed to mobile search campaigns, which according to PM Digital "represent a growing slice of the total paid search pie but which cost a fraction of regular search ads."
And there's more good news: revenue (at least for those merchants surveyed) was up a whopping 34 percent - although much of that increase can be attributed to some important holidays including Memorial Day and Mother's Day.