Interesting paper I was pointed to today:
arxiv.org/abs/1103.6038v1
We performed an image search on Yahoo for "Comet Holmes" on 2010 April 1. Thousands of images were returned. We astrometrically calibrated---and therefore vetted---the images using the Astrometry.net system. The calibrated image pointings form a set of data points to which we can fit a test-particle orbit in the Solar System, marginalizing out image dates and catching outliers. The approach is Bayesian and the model is, in essence, a model of how comet astrophotographers point their instruments. We find very strong probabilistic constraints on the orbit, although slightly off the JPL ephemeris, probably because of limitations of the astronomer model. Hyper-parameters of the model constrain the reliability of date meta-data and where in the image astrophotographers place the comet; we find that ~70 percent of the meta-data are correct and that the comet typically appears in the central ~1/e of the image footprint. This project demonstrates that discoveries are possible with data of extreme heterogeneity and unknown provenance; or that the Web is possibly an enormous repository of astronomical information; or that if an object has been given a name and photographed thousands of times by observers who post their images on the Web, we can (re-)discover it and infer its dynamical properties!
  