MissionClock has been in the iTunes App Store for a few weeks now, and I thought I'd post some sales information. The chart below shows the relative number of unit sales per day from July 30, 2009 to September 10, 2009. The two big spikes in sales corresponded to the STS-128 launch attempt on August 24, and the actual launch on August 28. Labor Day was particularly bad. There is no data for the dates from August 5 to August 8.
Clearly, launch days are good for MissionClock.