An article in strategy + business, Summer 2008 at 42, mentions that many Human Resources organizations track the number of job offers made by the law department and accepted. Such a metric might be insightful for large law departments that with some regularity bring aboard new lawyers.
It would be hard to say, however, in which direction you would like the metric to trend. If you are seeking the best applicants possible, you might end up with a relatively low acceptance rate. If you set your standards at a lesser level, you could boost the acceptance rate.