I spent the morning breaking software that has worked for months, by attempting to track down bugs in our simpleXY object-finding and measuring software for astronomical images. I failed to find the bugs, and left the software worse than when I started!
In the afternoon, Nitya Kallivayalil (Harvard) came into town and we discussed the issues involved in measuring statistical proper motions. She is the world's expert, because she has measured the proper motions of the LMC and SMC by comparing stars to quasars in HST images separated by two years. Now the question is: Can we do much more with heterogeneous data (which are worse than HST data) separated by much longer baselines? The issues are severe, especially when we think of the holy grails of the Sagittarius stream and other Milky Way substructure.