http://forums.station.sony.com/eq/posts/list.m?topic_id=125369

To help celebrate the season of Frostfell, starting 12:00 noon PST, Friday, December 21, 2007 and remaining until 11:59 pm PST, Tuesday, January 1, 2008, adventurers will be surrounded by a frosty bonus experience increase of twenty-five percent. Enjoy!

$$$$$$

will this stack with LoTD and exp pots?

I expect that it will. Exp potions stacked with the bonus from the "double exp weekend" following the widespread rollbacks a while back.