Duolingo has done my lessons for me.
I finished my Language 'skill' today, unlocking Abs. Obj. 1 and V. Pres. 3 in the German tree. I did this in offline mode, but when I connected back to the internet, the first lesson was completed for the next two skills.
While I shouldn't complain at 'free' progress, and I can always redo the lessons, I feel a little cheated. Was this an intentional part of Duolingo's programming or a bug?