If you read all of Matthew you get the impression that Jesus was saying to forgive them beyond your wildest dreams. God was not saying, "yah after this exact number you should forget them they are lost."
No what God is saying is that our human minds think 7 is a pretty decent amount of charitable forgiveness. But to really be Christlike and a true brother we must forgive beyond what we consider charity. We must go above and beyond what we consider good.
When you think about it, if God only forgave you 490 times, I think the same week I accepted Jesus as my savior I would be damned to hell again. This is why I am glad of his eternal grace and love. Something I still don't understand.
And I don't believe we are saved and forgiven through works. I believe we are saved and forgiven through the Son of God, Jesus. The 490 times I forgive someone doesn't even compare to that cross...