I'm sure most of Heroes fans are eager to know how many copies of Heroes5 and its addons was sold since game's release. After all, future of the series mostly depends on financial success of this particular game.
So, by official information from 12.2007, in Russia, CIS and Baltic States, HoMM5 sales exceed one million copies. Including addons and special editions, but excluding Gold edition which was released later. source

However, before you start calculating, I would like to note that in mentioned countries one copy price vary from 12 to 17 US dollars.

As for world-wide sales (excluding CIS), there is no official info, and therefor, exact numbers, but it was mentioned (not by UBI) that they are greater than CIS sales. Which in total gives more that 2 million copies sold.