Apart from bureaucracy and money, two fixed items that won't go away, I would say that landing at a strange airfield, (strange as in I've never been there, not strange as in the runway is underground) is still my biggest challenge. Well it's not a challenge as such but it's the area of flying that exercises my brain the most and gives the most satisfaction after a correctly flown approach and landing.
So, I need to force my time into ensuring I get enough and proper preparation done before each flight.
Ah I'm glad it's not just me then. Have you noticed that whatever time you turn up at the airfield, it could be three hours before you plan to take off, you still finish up with a 'Gotta get a move on' attitude as you're walking out to the a/c?
I still dream of walking casually out, strapping in with relaxation and leisurely going through the checks. Never seems to happen.