Greg,
      The current situation is more extreme than what went on in the past.
In the past one would get people who were trained in math, or physics, or
engineering, who would then switch over to economics and import their
methods from their previous background.  But they would actually switch
over formally to economics.
      Today we have a quite different sociological situation going on.  A 
lot
of these people are fully practicing physicists, in physics departments, not
switching to economics.  Furthermore, much of this literature is being 
published
in physics journals that are not indexed in the JEL, with the upshot that 
most
economists are not even aware that it exists.  Some of these journals 
include
Physica A, European Physical Journal B, and Physical Review Letters E.  One
finds grad students getting Ph.D.'s in physics whose topics are physics 
models
being applied to financial time series.  (BTW, Physica A is edited by H. 
Eugene
Stanley, widely recognized as the neologizer of the term "econophyics" a bit
over a decade ago).  I do not think we have ever seen anything like this 
before,
and I suspect that it is not a stable (or long-run equilibrium) situation.
      My more expanded views on this are contained in my New Palgrave
entry on Econophysics, available on my website at 
http://cob.jmu.edu/rosserjb.

Barkley Rosser