Until a few months ago you could expect a new Google Zeitgeist some 2 weeks after the previous month ended. That changed with the October edition (see
No monthly Google Zeitgeist anymore? Last one is September [webmasterworld.com] thread). Around December 18th a combined October/November edition was released.
Now it is already February 2nd, and still the no December edition (although there is a 2003 Year-End Google Zeitgeist [google.com]). So Google Zeitgeist is now bimonthly updated?