In Silas Marner, what did the people at the party think of Godfrey and Nancy?

In chapter 11, the party serves as the setting of one of the most poignant encounters between Nancy Lammeter and Godfrey Cass. Keep in mind that the Lammeter and the Cass clans are two of the most influential families in Raveloe. Like it often occurs with small, cohesive towns, some families with property, rank, history or money tend to stand out over the common folk. In that fashion, the townsfolk often imagine the spirit of greatness that accompanies these families will be perpetuated by joining their children in matrimony.
This being said, the townspeople saw the way Godfrey and Nancy were together at the party, although at the same time they were not so into each other that their actions would be too obvious. They referred to this behavior as "sweethearting."

I see he's for taking her away to sit down, now they're at the end o' the dance: that looks like sweethearting, that does."

Basically, in traditional "townfolk talk" the people are noticing both young persons want to get closer to one another. They see that they are getting closer physically and emotionally. The dynamics that could later turn into a full-fledged relationship are all there. Marriages and celebrations are big deals in traditional settings, so the blossoming of a relationship, especially one which would be quite popular, is always a topic of choice in a place such as Raveloe.