"Even In Eretz Yisroel"
(Picture courtesy of 613.org)
I spoke to the Clevelander Rebbe who said that he thinks that other groups do observe Nittel in January. As to which day to observe, one should follow his mesora, otherwise he felt that December 25th was the day that should be observed. He re-iterated that the power of the klippos is misgaber, gets stronger, and they have the power to sap from our learning at this time so he holds that one should observe Nittel even in Eretz Yisroel.