It's a terrible idea to try to learn theorems by memorization, if all you want to do is pass math tests fine.. but if you want to understand mathematics it's definitely going to do more harm than good.
You don't learn things from flash cards, you fix things you have already learned into your memory. And memorizing the formulas encoding theorems is definitely helpful.
Spaced repetition is a powerful learning tactic, and Anki is a good tool for it. There are some LW-relevant Anki decks here. But I wish there were more.
Which sets of knowledge are (1) likely useful to LWers, and (2) straightforward to encode into Anki decks without needing to be familiar with that field?
Some examples:
Which other sets of knowledge would you like to see Ankified? Please link to the actual knowledge set you'd like to see encoded.