  We present the first results from our high-precision infrared (IR) astrometry
program at the Canada-France-Hawaii Telescope. We measure parallaxes for 83
ultracool dwarfs (spectral types M6--T9) in 49 systems, with a median
uncertainty of 1.1 mas (2.3%) and as good as 0.7 mas (0.8%). We provide the
first parallaxes for 48 objects in 29 systems, and for another 27 objects in 17
systems, we significantly improve upon published results, with a median (best)
improvement of 1.7x (5x). Three systems show astrometric perturbations
indicative of orbital motion; two are known binaries (2MASSJ0518-2828AB and
2MASSJ1404-3159AB) and one is spectrally peculiar (SDSSJ0805+4812). In
addition, we present here a large set of Keck adaptive optics imaging that more
than triples the number of binaries with L6--T5 components that have both
multi-band photometry and distances. Our data enable an unprecedented look at
the photometric properties of brown dwarfs as they cool through the L/T
transition. Going from \approxL8 to \approxT4.5, flux in the Y and J bands
increases by \approx0.7 mag and \approx0.5 mag, respectively (the Y- and J-band
"bumps"), while flux in the H, K, and L' bands declines monotonically. This
wavelength dependence is consistent with cloud clearing over a narrow range of
temperature, since condensate opacity is expected to dominate at 1.0--1.3
micron. Interestingly, despite more than doubling the near-IR census of L/T
transition objects, we find a conspicuous paucity of objects on the
color--magnitude diagram just blueward of the late-L/early-T sequence. This
"L/T gap" occurs at MKO(J-H) = 0.1--0.3 mag, MKO(J-K) = 0.0--0.4 mag, and
implies that the last phases of cloud evolution occur rapidly. Finally, we
provide a comprehensive update to the absolute magnitudes of ultracool dwarfs
as a function of spectral type using a combined sample of 314 objects.
