According to the AICPA, the third quarter of 2007 by far had the highest candidate passing rate. BEC was the only exception and it was lower than the 2nd quarter by less than 1%.
The worst time to take the exam? January/February.
The difference between the third quarter passing % and that of the 1st quarter is staggering.
AUD: 6.82% higher
BEC: 3.29% higher
FAR: 8.73% higher
REG: 8.27% higher
Combining this little nugget with a previous post, statistically, you are more likely to find success on the exam if you take two sections during the window of July/August.
This shouldn't tangibly affect anyone's exam prep or test scheduling, but it is somewhat interesting.