Directory limits

[Roger A Safian <r-safian () NORTHWESTERN EDU>]

We have a limit the number of returns when looking up entries in our directory of twenty.  We've had this limit, or 
something like it in place since we discovered fire.  I always thought this was fairly typical.  Recently we have been 
asked to justify that choice.  As part of that, I'm wondering now, what do others do.  Is this pretty common?