Possibility of having word lists once lessons are completed?
Is it possible that there could be a feature implemented that allows users to review word lists (such as verbs or animals) after completion of a package? What I mean by this is that once a language pack has been completed (i.e. pres verb 1) a list would become available where a user could merely hover over a word and hear the pronunciation as well as see the spelling. Thus offering even more reinforcement via repetition. If this is not possible, I would just like to say that DuoLingo is one of the best websites/mobile applications to have been created to date. (And I would most assuredly not hold this one rather superficial request against you!) :D
You can already do this in the Words tab, which lists all the words you have learned.
The only problem with this is you cannot filter the words for a specfic skill or group of words, although you can sort the list in several ways. This means that you may have to scroll through over 1500 words to find the one you are looking for.
Another filter option that I would urge to consider: Sorting by word frequency. (Per official sources, i. e. for English see: http://en.wikipedia.org/wiki/Word_lists_by_frequency#English)