Jon Udell continues to do great work showing how hard it can be to get (seemingly simple) data - an awful lot of it is locked in a trunk or simply not available online. Take temperature data:

Given all that’s been said and written about climate change, it turns out to be surprisingly hard to get hold of historical climate data. I had to look around quite a while before I found this FTP site where NOAA has parked files full of raw temperature and precipitation data.

He's also blogged recently about crime statistics, which are apparently even harder to get (I noticed this morning that there's a dispute in Baltimore about crime data). It sure would be nice to simply have raw access, so we could draw our own conclusions.