Now, how many celebrated yesterday, on the 24th? I know Scandinavia and big parts (if not all) of Germany does. Any more countries?
Yes, in Sweden we do everything on 24th. Most of us have a few days off including this date (usually extra payment if you work on it, as if you work during the weekend), all the schools takes a holiday 1 or 2 days before 24th which lasts for around 2 weeks. We open the presents, eat the christmas food and everything. 24th (christmas eve) is simply the day we call "Christmas".
EDIT: I know also the royal family of UK celebrates on the 24th, by reading from wikipedia.