Reddit, where he's currently hosting an Ask Me Anything thread. Personally, we find Super Hexagon to be "beyond ideal for the mobile format," so its success isn't a huge surprise.
Cavanagh is looking to make Android, PC and Mac ports of Super Hexagon, and maybe even one for Blackberry Playbook, since a friend of his has one of those. Sales on iOS have been "way beyond expectations" so far.
"I didn't see that coming at all – I'd really gone into this expecting the game to be a super niche thing that only a tiny handful of iPhone gamers would be interested in, and I'm really glad to be proven wrong," Cavanagh writes.
In other news, Cavanagh is interested in board games and has built two, "but neither are very good yet." To learn more about this, Cavanagh's take on Steam Greenlight, or to ask your own question, hit up his Reddit AMA post.