Roger,
I searched my Bibliography for Designing Lead-Free, RoHS-Compliant, and
WEEE-Compliant Electronics at
   http://www.dbicorporation.com/rohsbib.htm
for "whisker", and counted 192 papers and web pages whose titles
directly refer to tin whiskers or Sn whiskers.  I probably have at least
another 100 papers that talk about tin whiskers.  I've seen at least a
couple of papers that talk about tin whiskers growing out of lead-free
solder joints after soldering, even when the components themselves had
been annealed at 150C for 1 hour after the leadframes were plated...

The earliest reference that I have so far found to tin whiskers is page
153 of Burns, R. M., and Bradley, W. W., Protective Coatings for Metals,
3rd Edition. New York: Reinhold Publishing, 1928.  It says:

"Zinc, cadmium, and tin, when used either as coatings or as solid metal,
may develop crystalline filaments called "whiskers."  Metallic in
nature, whiskers are single or twinned crystal growths of about 80 x
10^-6 inches (2 microns) in diameter and up to 3/8 inch or more in
length.  They appear under a wide variety of environmental conditions,
including vacuum of 10^-8 mm pressure; they have been particularly
troublesome in low voltage communications equipment where their low
electrical resistance provides leakage paths between components, one or
both of which are coated with one of the offending metals.  No trouble
of this sort is experienced with components between which potentials are
in excess of about 10 volts, this potential being sufficient to "burn"
the whiskers off.  Whisker growth does not depend on the existence of an
electric field; hence it can proceed during idle or storage periods.
Normal auxiliary coatings, such as paint and enamels, are ineffective in
preventing this phenomenon.  The mechanism of whisker growth has
received considerable study."

My personal plan is not to buy *any* new electronic products or
equipment between January 2006 and June 2007.  By July 2007, with
billions of people as the subject of this little "experiment" by the
European Parliament for a year, we might know whether *some*
RoHS-compliant electronics can remain safe and reliable in at least
*some* environments for at least their warranty period...

But I'm not betting on it, even then.  Instead I've already invested in
over 70 pounds of 63-37 and 60-40 tin-lead solder of various gauges and
fluxes, to keep my own and close friends' electronics stuff working.

                John Barnes KS4GL, PE, NCE, ESDC Eng, PSE, SM IEEE
                dBi Corporation
                http://www.dbicorporation.com/

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