I don't know. I believe that giving tips is a very good custom and even if everything was just awfull you should give at least 5%. It's better to give tip to someone who doesn't deserve it than not to give to somebody who does indeed deserve it.

But that is just what I think. I don't follow this rule myself. If I'm short of money I don't leave tips even if I was served like a king :)

Anyway people who serve you in Russia may have different expectations from Americans than they have from Russians.