I have read some on forums and read alot about khorne berzerkers. i will print a damage table for khorne berzerkers here:
Infantery II Vehicles II Buildings. II Deamon II
armour Med High H.Med H.Hi Cmdr Low Med High Air Low Med High Med High
DPS: 36.5 36.5 36.5 36.5 19.9 13.3 10.5 6.6 2.4 5.0 3.3 2.4 21.2 6.6
As you can see they are poor versus turrets (who have low to medium building armour) and poor against vehicles. The problem is to get vehicles at the time he gets berzerkers. I don't remember if necrons turrets are effective against infantery, i guess they are not. If they are effective you can hold him away from your base untill you can get vehicles and then turn the battle. I guess its the same tactic for almost all teams. If you want to see if your enemy really IS doing a berzerker rush i guess its worth to sacrafice a worker (if you are eldar, as i am) to see whats happening in his base. So you need to learn how the upkeep of a berzerker rusher looks like to be able to see if he really is going to preform it.
I think that necrons have the hardest time to counter a berzerker rush, since their turrets are not as effective and their infantery are vurnable to their extreme damage and moral immunity. I hope this damage table can help you to come up with a tactic.
I got this information here: http://wiki.reliccommunity.com/Khorne_Berzerker_Squad