Disappointingly, but perhaps not entirely surprisingly, half of our respondents (from 22 gamers) had not even heard of itch.io. 22% had purchased a game from them, and another 6 had never purchased a game but had at least heard of them. Hopefully more gamers will be aware of them soon... (Of course I didn't ask if people had downloaded a free game from icth.io, and there are plenty of free and "pay if you want" games there, so some of those 6 may have got games from itch, just not paid for them.)
From the meagre set of 5 developers who responded, only one had sales in the 200-499 bracket, with the other 4 all selling less than 10. Again I didn't word the question very well perhaps - this could include zero sales.
At any rate, the responses haven't filled me with hope, so I have a request to #indiegame fans - please retweet or otherwise share games you've found and enjoyed on Itch.io and help make it better known!