Predictions for the angular distribution of massive quarks and leptons
are presented, including QCD and QED corrections. Recent results for
the fermionic part of the two-loop corrections to the electromagnetic
form factors are combined with the BLM scale fixing prescription, Two
distinctly different scales arise as arguments of alpha(s)(mu(2)) near
threshold: the relative momentum of the quarks governing the soft glu
on exchange responsible for the Coulomb potential, and a large momentu
m scale approximately equal to twice the quark mass for the correction
s induced by transverse gluons. Numerical predictions for charmed, bot
tom, and top quarks are given. One obtains a direct determination of a
lpha(V)(Q(2)), the coupling in the heavy quark potential, which can be
compared with lattice gauge theory predictions. The corresponding QED
results for tau pair production allow for a measurement of the magnet
ic moment of the tau and could be tested at a future tau-charm factory
.