Thanks to Fink, I got healpix working and started making Sam his perfectly uniform sky catalog for automated astrometry. I made a healpix grid with Nside=64 (49152 pixels), and am keeping the brightest 1024 USNO stars (subject to R>14 mag) in each pixel. I return the full, all-sky list in brightness order, from brightest to faintest. So Sam will get a very uniform all-sky catalog with a full brightness ranking.
It would be nice, philosophically, if we could operate astrometry.net (both server-side and client-side) with no reference to specific brightnesses beyond ranking. This would relieve our users of anything approximating calibration (or even nonlinearity correction).