I would suggest you create your own decks with images you find or create yourself rather than downloading existing decks. Memorization is generally improved by this approach (see Higbee, Your Memory : How It Works and How to Improve It).
I also like how Anki has spaced repetition built in nicely.
Plus what makes Anki awesome is the ability to use the cards on every OS, making it a ideal collaborative tool. But as mentioned by tom_b you need to create your own decks. There is very little use for most public decks unless you have the extreme lucky moment having to learn exactly the same as the author of the deck did.
In fact this might be a more interesting place for innovation - the management of Anki cards. Not sure how the market situation looks but you could be offering cards for popular textbooks or create a marketplace for these in order to rise the quality. Not sure how the copyright situation looks like, but you could be entering also a more mainstream market - for example by offering a card deck for each issue of Mental Floss in order to learn at least a few interesting things each month.
http://itunes.apple.com/us/app/ankimobile-flashcards/id37349...
If you can duplicate the benefit and make the UI simpler (e.g., simplify it down to two buttons: I got it right / wrong), and make it cheaper, you have an ok chance to do well.
As for the app, go for it! Just don't use it for math and preferably don't pitch it as a aid for math students. You'll only be hurting them.
notecard.herokuapp.com
You can create an account (no email verification necessary). Your first step is to create a semester, then a section, then you create notecards. The notecards flip front to back with a single click. You can also put your notecards in a "Known" or "Unknown" pile so you know what you have to study.
edit: The notecards also support HTML
Provide people a way of creating the flash cards online. Let them use a simple editor or type html directly. Make sure they can do it quickly.
Have the app connect to your web service and pull down the card groups and cards. Of course, they should be able to edit the cards on the device as well.
Swipe left/right to cycle through full screen cards, tap to flip them over.