As a seasonal business, the most common comparison I make is not with the previous period (ie, November 2011 vs December 2011), but rather with the same period in the previous year (December 2010 vs December 2011).

The current UI forces me to cut and paste dates, then change the year in both the from and to boxes.  This is a real PITA when I have to do it over and over again, many times per day.  I is frustrating because all it would take is a simple checkbox "compare to same period in previous year" to pre-populate those dates for me.

This should be a very simple change -- please consider implementing it as soon as possible - I think a great many Google Analytics users would benefit from it.