I've been using it for about a week, but over 100+ cards a day. I'm addicted!
I was expecting a badge or something saying "You've mastered 50 words" or something like that. Or maybe "You've met your practice goal 7 days in a row." Like @oulenz, I am also from Duolingo, but I am here to stay! I haven't been here long but feel that I am learning so much more and at a much faster rate.
Right now, I track my progress by seeing how many new words I've learned and seeing my percentage.
On a side note, if there a list of words that I've already learned with their translations somewhere?