Leveling?

[kundalini]

I shoot visually level with the aid of the gridlines in the viewfinder. I don't worry about being "dead on" since it is too easily fixed in post. A good reason (for me) to shoot a little fat.

 

[enzodm]

The one that bothers me the most, is when I see a photo with water on the horizon and it's not level.

It creates a visual tension...it prevents the viewer from being able to enjoy the image like they should.

I agree. It is the first discriminant between snapshot and something closer to a photograph. Said that, I like to level basing to the scene (although at short focal lengths sometimes you have to choose direction).