A way to revolutionize practice sentence generation?
Under each word page in the vocab section, why not put an add a sentence button for each form of the word and either have the DuoLingo staff approve the sentence you have contributed so that everybody else gets that particular sentence in their practice (I suggest this method)... Or have users flag sentences as good or bad (THEY have to be completely punctuated, which maybe a problem with this method...)... I strongly suggest the former, and remember, they NEED to be punctuated... They sentence must also consist of already learned vocab (this can be placed in the algorithm rather than criteria to approve, because if a new word is not in the database, no users will receive the sentence anyway, so that when the word is put in the database, the sentence can be practiced for all users, with the word perhaps being a new word, rather than being refused altogether.)
@christian - the point about human computation (http://en.wikipedia.org/wiki/Human-based_computation) - is that it refines quality from quantity. Of course, it's the idea behind Captchas and Duolingo group translation. Now you wouldn't necessarily use human computation for selecting the best user-created example sentences, but the site software could still facilitate us as a group selecting the good ones.
@christian "Note that producing correct L2 output is infinitely more complex than translating into your L1." [Not sure how to markup a quote in these text boxes.] Yes, this is a very valid point. Perhaps then have the native French speakers generate example sentences for the English learners and vice versa? Of course, you need to have courses happening both ways for this to happen but they do already have that for the Spanish/English pair.
@mikeydee Since you're on a humility kick, I suggest your clarity of expression could do with some attention too :P But yes, good suggestion :)
I gave it some extra exposure on reddit - http://www.reddit.com/r/duolingo/comments/wumuv/luis_responds_in_the_affirmative_to_a_suggestion/