  Because Spitzer is an Earth-trailing orbit, losing about 0.1 AU/yr, it is
excellently located to perform microlens parallax observations toward the
Magellanic Clouds (LMC/SMC) and the Galactic bulge. These yield the so-called
``projected velocity'' of the lens, which can distinguish statistically among
different populations. A few such measurements toward the LMC/SMC would reveal
the nature of the lenses being detected in this direction (dark halo objects,
or ordinary LMC/SMC stars). Cool Spitzer has already made one such measurement
of a (rare) bright red-clump source, but warm (presumably less oversubscribed)
Spitzer could devote the extra time required to obtain microlens parallaxes for
the more common, but fainter, turnoff sources. Warm Spitzer could observe bulge
microlenses for 38 days per year, which would permit up to 24 microlens
parallaxes per year. This would yield interesting information on the disk mass
function, particularly old brown dwarfs, which at present are inaccessible by
other techniques. Target-of-Opportunity (TOO) observations should be divided
into RTOO/DTOO, i.e., ``regular'' and ``disruptive'' TOOs, as pioneered by the
Space Interferometry Mission (SIM). LMC/SMC parallax measurements would be
DTOO, but bulge measurements would be RTOO, i.e., they could be scheduled in
advance, without knowing exactly which star was to be observed.
