Finally I got the new AIR International, which includes an article by Aleksandr Mladenov on the Mi-28N.
He writes that until late 2012 more than 50 Mi-28N (plus 7 pre-production helicopters) had been delivered to the VVS, of which 2 have been lost in accidents. In total 120 are to be acquired, from 2016 onwards the Mi-28NM will enter service with the older helicopters planned to be upgraded to the new standard.
The trainer version, the Mi-28NU, will be available sooner, until 2015.
As all current Mi-28s lack a radar, they mainly rely on their FLIR during exercises and maneuvers. It has a range of 7 km, while the NO-25 radar of the Mi-28NM shall be able to detect targets 20 km away from the helicopter. The usual attack tactic is to dive on a target, as firing missiles while hovering is considered ineffective (I don't know why).
Finally, the Mi-28N is compared to its rivals, the AH-1, AH-64 and Tiger.
I'm not sure whether the data given is correct, according to it the Mi-28 only has a max speed of 300 km/h and a max weapons load of 2,4 tons. Its combat radius is 200 km, what is way less than that of the AH-64 (480 km).