Still working on Bitwit, my CS/math spaced-repetition education site [1]
I'm dogfooding it heavily. The bugs at this point tend to be in card formatting. I ended up delaying the introduction of TeX/MathJax until I had quite a few cards written, and man oh man, it's tedious to go back and fix that formatting in hundreds of cards.
The real question: does it work? I _think_ so. I'm learning, and I feel like I'm retaining more, and I think the general structure counteracts or compensates for most of my issues as a learner. I think the science is pretty solid, but I'm also experimenting in a few areas, so... eh, we'll see.
If anyone is interested in trying it out, you can use it for quite some time (several months, maybe a few years) without needing to provide an email address or sign up.