I didn't know about this holiday! It's an american day and I'm not american but I'm going to plug it anyway. I first learned of it over here,Bore Me To Tears: Happy Reason Day!.
Now yes, I'm a theist. And I'm a theist who thinks prayer is a perfectly reasonable thing to do. But I'm also a lefty, liberal theist who happens to think a national day of prayer is a ridiculous thing meant to pander to some americans and exclude others. The National Day of Reason is a nice counter.