I'd estimate 15-20% of downloads have been paying, and I've been lucky enough to have both ratings and reviews in the double digits, with at least one review of the kind that every creator hopes the criticism gods will bring them if they've been good - an ideal customer who really gets the philosophy behind the product.
And here's something else to consider: In the game writing field, we are all facing the Crafter's Dilemma. To illustrate, one of my other hobbies is crochet. I make scarves and hats; they're nice. Every once in a while someone will see one of them and say, "You should sell these!" But here's the thing: I can't possibly charge what they're worth. Between materials and the time I put into them, even paying myself minimum wage, no one would ever pay what the calculation comes out to. A gift economy is the only thing that makes sense.
I do feel my products are worth more than what I have made from it, but I am actually surprised that anyone decided to pay money for these.
...I am a little sad about the % of paid vs free (6.8% on the first, 8% on the second, and 2% on the third), and I would love to get any sort of review on them. Getting reviews on anything that isn't on the "Best Seller" part of the front page seems to be difficult.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.