For a while I had been struggling with a strange overdensity of M-dwarfs in the BoRG survey. It felt as a strange coincidence or a fault in the identification process. Thanks to Bob Benjamin, I finally got a positive ID on what could be causing the overdensity: the Saggitarius stream. Even the distances of the bulk of M-dwarfs in that particular field fit nicely with the typical distance to Saggitarius dwarf: 20-25 kpc.
To me this revealed a big gap in our knowledge of the Milky Way. Suppose you are a extragalactic astronomer and find some odd over-density of point sources. Before you write the paper on some z~8 cluster, you need to check there is no stellar stream surrounding the MW of any kind in the vicinity. But a decent map collating all the known streams, arms, satellites and globular clusters and their tidal features etc does not exist yet. My solution: email Bob but there has to be a better one.