I'm happy with the calendar year on AS.

A couple years back, HHonors tried the rolling qualification thing and it was a complete nightmare.

Perhaps it was in their implementation, but it turned into a confusing mess, with questions over 12 month versus 13 month status and other things. Take a look at the posts on the Hilton forum a couple years back and you can see it.

It probably chased more people away from HHonors than it brought into the fold.

Calendar year is simple and it works.