While the answer matters, it's the hesitation or the enthusiasm of the respondent that's critical. Manager to manager, this one question can reveal more than any other kind of reference check. When you're hiring, don't pay lip service to the importance of reference checking. Involve the people who will work with the new hire. If they fail to meet the deadlines they set more than twice, start talking to other employers, because there's likely a profound management problem that you can't see.
Companies lose good candidates when they hesitate to make decisions.
Granted, the interview and decision process takes time. But there is no excuse for not having a decision schedule and sticking to it. The price you pay for treating your hiring process indecisively and your candidates disrespectfully is a bad reputation. Set a hiring and decision schedule and stick to it. If you can't decide on a candidate, then call the candidate and tell him you have no plans to make an offer at this time.