This observance is held in parallel with the National Day of Prayer, on the first Thursday in May each year (May 7th in 2009). The goal of this effort is to celebrate reason—a concept all Americans can support—and to raise public awareness about the persistent threat to religious liberty posed by government intrusion into the private sphere of worship.
The Day of Reason also exists to inspire the secular community to be visible and active on this day to set the right example for how to effect positive change.
Unfortunately, the list of events page shows the day hasn’t quite taken off yet, as there were announced events in only a handful of states. But it’s a start.