Thousands and Thousands

Those who claim that a thousand is always a thousand (see last post) have probably not done a study even of the way that the Bible uses the word "thousand". Here's an interesting test text for the literalist view

Deu 7:9 Know therefore that the LORD thy God, he [is] God, the faithful God, which keepeth covenant and mercy with them that love him and keep his commandments to a thousand generations;

Taken literally would this not set a minimum limit of the number of generations of humans? After all if there is a single person who loves the Lord, he will be faithful to to a thousand generations of their descendants. Or is the intent of the text to say "a very long time"?

Suppose a generation is about 25 years and if a thousand is always a thousand then God will keep covenant and show mercy for 25,000 years. Yet, Abraham loved God and he lived less than five thousand years ago. By this there are 20,000 years left until the end of God's mercy.

Or is God's mercy everlasting and the word thousand means a big number once again (like the cattle on the thousand hills)?