Just enough to be dangerous....

A colleague and I were talking this morning about what knowledge depth is desirable in referees.  A reviewer who does not know an area in detail will sometimes give a bold or unconventional idea a fair, unbiased hearing.  In the other limit, a reviewer who is a hardcore expert and has really pondered the Big Picture questions in an area can sometimes (not always) appreciate a new or creative approach that is likely to have big impact even if that approach is unorthodox.  Where you can really run into trouble sometimes is with reviewers who know just enough to be dangerous - they can identify critical issues of concern, know the orthodoxy of a field, and don't necessarily appreciate the Big Picture or potential impact.  This may be the root of the claim I've heard from journal editors, that often the "recommended referees" that people suggest when submitting articles end up being the harshest critics.  Just a thought.  In general, we are all well served by getting the most knowledgeable referees possible.