Strangely enough I too remarked only the other day how the bag drop-off lines are becoming longer whilst the conventional check-in lines are getting shorter. This with the exception of Germany as a majority of Germans still seem to favour the conventional procedure.
Amsterdam have a self bag drop system now and it's quite a fast process once you're used to it.
Otherwise, a trick to use is to assess which line is the shortest. If it's the full check-in line, take that one (even if you've checked in online). When you get to the desk just say that you coundn't print the boarding pass and that's why you've come to the full check-in section. This procedure is NOT valid for the likes of Ryanair of course!