Yeah me too... I beleive it is like the time when it was made? Like the older stepings are older technology and the newer stepings are a bit better and has better cooling... not sure what determines the steping (the variable)
Stepping is basically the version number of the processor. As the letters and numbers get higher, that means it's been more revised since the original product. The original is typically A0. http://en.wikipedia.org/wiki/Stepping_(version_numbers)