I've never understood this system of penance in RC tradition. Usually this penance is to say a prayer and that's all, nothing in connection with the sins you've committed, with your weaknesses. That's not a good way to improve ourselves and develop our spirituality.
Fortunately, a few years before my conversion into Orthodox Church, I had a really good confessor, whose penances given to me were in some way "Orthodox" - I mean they were more like a spiritual exercise, then a punishment.
I Slavic tradition the situation is the same as in Greek Orthodoxy. As ozgeorge said, the aim of the confession in Orthodoxy, is change ourselves for better. That's why it's a good thing to have a regular confessor, because he knows our weaknesses and by some advices, regulations of prayer rule and the frequency of participating in Sacraments can help us better.