http://www.fangraphs.com/blogs/what-...entional-walk/

Dave Cameron provided some good research here

Looks like hitters don't typically hit that well after an IBB

Summation

There are certainly times when the IBB does backfire, and I wouldn’t use this data to suggest that the IBB is always the correct decision. There is a real cost to giving the opponents an extra baserunner, and there needs to be a substantial increase in likelihood of getting an out in order to offset the larger potential for an extra run to score from giving the opponent a free baserunner. However, I do think the data suggests that IBBs do serve a strategic function, and can reduce the odds of giving up a run in a situation where preventing one run is of the utmost importance.