Just to make sure everyone sees this now that the Nature issue is out so they could post the PDF:

A single sub-km Kuiper Belt object from a stellar Occultation in archival data

Schlichting et al. filtered 4.5 years of what would normally be considered engineering-level telemetry from the HST fine-guidance sensors to fit the diffraction pattern expected for a small trans-Neptune object occulting a guide star, and find a single strong candidate (most likely diameter near 1.0 km) This is said to be far enough below some predictions to rule out distributions in size which are strongly weighted to smaller objects in the ~km range. (This got my attention mostly for being such a nice use of archival data.) There is also an STScI press release.

Well less than a kilometer in size is an amazing observation knowing it orbits our Sun at a distance of 45 AU
Same story here with artist’s impression:
http://www.astronomynow.com/news/n0912/17kbo/