I'd love to hear what others think, because I think there are different practices that can work for different people.
I prefer to make my own because just the act of deciding what to put on the card, how to write it out, and then actually writing it out gets me 50% to my goal (of remembering the information).
Also, it's super-important to remember that you really don't want to put an entire problem on a flashcard. You're using flashcards to help you memorize or recall certain information when you see a certain trigger. Your goal is never to memorize a specific problem!
If you want to remember an important aspect of a problem, then figure out what the clue or trigger for that aspect is, and put that on a flashcard. Think about alternate ways that the clue could be presented, not only the way that it was presented in this one problem.
Take a look at the discussion in this article about the "when I see / I'll think do" method of building and using flashcards:
http://www.manhattangmat.com/blog/index ... -the-gmat/Next, when using the cards, remember that they should be "living" documents. When you've learned some, they get retired to an "I've already learned you" pile. You can move something to this pile when you've nailed it 3 times in a row while reviewing a stack of flashcards. (And that 3 times in a row can't be the same day - spread out over enough time that you would actually forget if you were going to forget!)
You'll pick up that retired pile once every 2-3 weeks just to make sure that you do still remember those. If you nail something 2 times after retiring it (meaning, you're looking at it 2-3 weeks later and then again 2-3 weeks after that), then you can retire that card permanently.
For the ones that are still in the main deck, you don't need to review them all at once. When you have 10 minutes, take a stack and do what you can in that time. Then set that mini-stack aside so that, the next time you have 10 minutes, you're reviewing something else. (Though if there were any that you REALLY didn't know, pull them out and stick them back in the main stack.) After you've gotten through most of them once that way, shuffle the cards and start all over again.