More often than not its a combination of camber on the bottom chord as well as the trusses being misaligned and then cut at the eaves to make it appear that the truss was not out of align.
The rare times I use trusses, I have had a couple companies put way to much camber on the truss to the extent that the bottom chord was off the interior wall top plates by as much as 1 inch. What framers also mistakenly do is to nail the bottom chords to interior walls which are a no-no. There are special clips for this however the truss companies never tell you about his nor do they send them out. The also don address the fact that when you use such clips you drywall will look like the picture that David posted (not to say that was the reason behind those cracks).
Speaking from experience, engineering and application do not always go hand in hand in the field.
In the case where my trusses were over 1 inch above the plates, I simply had my framer cut the chords, properly sister it, had the truss engineer stamp it and then back charged the truss company over $1000.00 for wasting my time.
Most of the time if I look long enough I can find problems with truss installations.
I am not a big truss fan.