So I insulated the walls on the 11th of this month (and piled more in the attic, too).  Xcel was nice enough to give me daily meter readings for most days during February, so I made a graph of usage vs. daily temperature. 

Unfortunately I don’t have readings for every day, so the lighter green bars are just averages for readings that spanned multiple days.  It’s not too dramatic, I guess; partly influenced by who was home and taking the thermostat off program, etc – and a therm is a pretty coarse reading.  Still, I think it is fairly apparent that gas usage dropped by a pretty significant amount.  Which is good, since that was the goal!