Depends heavily on the aircraft. I know for a fact that a lightly
loaded DC-10 will not be able to
land and stop at McCarran with a 10+knot tailwind. Been onboard when
it was tried and
remember going off the airport boundries at less than 30 AGL You get a
new perspective on
things when you see TV antennas go by above you and chimmneys just
below you!

Lockheed L-10A is virtually impossible to land safely with any
tailwind. It has so much tail
surface that it either slams the tail down or tries to put it on the
nose.

deHaviland Super Chipmunk with a Krier tail gets super squirrelly with
any kind of tailwind. Of
course the tail will come off the ground at about 15 knots forward
speed