It is a problem that sometimes occurs - basically the sensor has been placed slightly out of alignment, so it is obviously recording at a slightly angle compared to the viewfinder (which is set straight)
A friend has this problem with his 350d, but since it is so far out of warranty now he just learned to live with it and compensate - either by just shooting slightly squint in the viewfinder, or purposely shooting slightly wider and cropping/rotating to the desired shot.
|Nowhere by Nanard 92|
from The Illusion of Depth and Distance
|Green Tomato by lim yau tong|
from Growing Fruit