Sure we all love using NL, but for a lot there's just one or two things that bug the crap outta you! What are yours?
Personally, I find it a little annoying when you go to save a small section of roller coaster (like the beginning, just station and dropout) and it warns that the track is too short. So? If the editor lets me save it anyway why do I need that warning!? I understand that warning being shown when entering the Sim, though.