John Dewan has an article at Bill James' website that examines the dramatic increase in the use of defensive shifts in MLB in 2012. Dewan notes that, while the shift was utilized 1900 times in 2011, teams are on pace to utilize a shift 3800 times in 2012, doubling the overall rate.
Dewan notes in his piece that this is one of the rare instances where lots of teams are almost immediately adopting a strategy that is supported by the analytics, talking about his own research on the impact of shifts, and listing the teams that are shifting most often, and least often, in 2012.
The team that shifts the most is, not surprisingly, the Tampa Bay Rays, an organization that is known for its progressive ideas. Tampa has employed a shift aggressively in prior years, but Dewan has them on pace to use a shift 695 times in 2012, more than three times their previous high. Nine of the top ten teams in the number of shifts used are A.L. teams, including the Rangers (at #10), and other organizations that are seen as very forward-thinking such as Toronto, Oakland, and Boston.
If the greater use of defensive shifts catches on, we could see a couple of different effects around MLB. Better defensive positioning, including more shifts, would cause a drop in batting average on balls in place, which would result in an overall drop in offensive numbers. Potentially more significant is that widespread adoption of defensive shifts would diminish the value of extreme pull hitters, who would see fewer and fewer hard hit balls fall in for hits. That could mean a change in the types of hitters who end up having success in the major leagues, with more slap and spray hitters who use the whole field, and fewer power hitters, which would change the dynamic of the game, along with also contributing to a potential drop in offense.