I'm a pretty heavy SuperMemo user. I put everything I learn into it, and I use it every day. I use Skritter every day as well. I'm wondering how they affect each other. I've been using SuperMemo before Skritter, so all the characters I learned the day before, I generally review in SuperMemo just prior to practicing them here. Will that screw up Skritter, or help it?

Practicing in both places will be less efficient than practicing in just one. Reviewing a character right after you've just actively recalled it won't increase your memory of it by very much.

That said, if you spend most time on hard items (where you get them wrong or have to think a while to recall them), then the second review in short succession will not take very long, and will be successful, so each hard item's reviews will be concentrated in one program or the other. Then, once the items get spaced out a bit more, you're essentially just reviewing items more frequently, leading toward higher retention rate (in SuperMemo terms, lowering your forgetting index).

But if you have set SuperMemo to 10% forgetting index, it's going to try to hit that 10% by reducing SuperMemo review frequency until you forget 10% of the prompts -- it doesn't know you're going to be reviewing in Skritter, too. Skritter will do a similar thing, although it doesn't adapt as much yet because not all the self-tuning is there.

So it'll essentially balance out a bit, but each program won't be able to schedule as well because you'll be short-circuiting it with the other, leading to a little more chaotic scheduling and a corresponding loss of efficiency. If I had to make an absurdly rough guess, I'd say that 30 minutes of SuperMemo + 30 minutes of Skritter =~ 50 minutes of just one of the two. (SuperMemo's scheduling is better, for now, but I'd bet that Skritter at least makes up the difference with more effective reviews -- and Skritter's scheduling will eventually be better than SuperMemo's.)

Eventually, we'll want to have data import/export all set up, so that you can move all your Chinese review from SuperMemo to Skritter or from Skritter to SuperMemo and keep all your practice history. The export may come in the near future, but the import will probably be a while.

I use Anki for training recognition (Hanzi -> English), while I'm using Skritter for producing (English -> Hanzi).

I find this combination very good. I usually spend ~30-40 minutes with Skritter in one or two sessions, and Anki wherever I get the time (mostly offline).