I love everything about your app except for the flashcards app. I mean, I REALLY like your app. But I REALLY don't like the flashcards part.
I think you could help your students much more by simply create decks for use with Anki.
If you're not familiar with it, Anki is a free OPEN-SOURCE app for flashcards. It runs on Windows, Mac, iPhone, and Android. I've used it for years before finding your program. You just have to create an Anki-compatible deck and let your users download it and import it into Anki.
Anki's use of Spaced Repetition is really important. When you answer a question, you mark a question/word/phrase as "Again," which means "give it to me again in a 1 min," "Good", which means "I have it, but ask me again in 10 mins," or "Easy," which means "ask me again in four days." A full deck can incorporate pictures, sounds, and is able to go either way (spanish-> english, english-> spanish).
You could easily create Anki-compatible "decks," as they're called, which could only be downloaded from your website. They would contain all the words, conjugations, and phrases from each lesson. I see you constructing the download just like you do w/the podcasts. Tell the interface how far along you are, and it downloads the appropriate deck for you. OR you could just create a deck for each level. That would work, too.
What I'm doing as I go through is I put into Anki (manually) any words I don't know cold. This is not my first time trying to learn Spanish, so I have a lot of it down already. When I have a few mins and don't want do a full lesson, I pull out Anki and work away.
It just xxxx I have to create the deck myself. If you at least took the time to create a deck for each level, and put it up on the site, that would help all your students so much.
Here's the best part: All you have to do is create a text file in the right format. Here is what you need to know: