Definitely the inconsideration of goons who don't have any notion of a photo line and continue to be as annoying as Maine mosquitoes. I think seeing no trains when you want them- especially when the lighing is particularly perfect- gives us a challenge to be more creative in how we can photograph railways, with focus on the physical plant, signals, etc. Changing film types, filters or exposure to compensate for uncooperative weather is also an interesting challenge.

I'd rather have pictures of employees in them then not. It's actually pretty challenging to get a good shot with someone working diligently at their craft, especially close up. Most are wary of railfans, and generally repelled by the sight of a camera.

Goons, though, definitely spoil it. Get your shot, stand out of the way of others, and be considerate. Chances are, if you spent a day's drive, and a couple hundred bucks to get there and back, the guy next to you did too.