Should be a number of threads on this subject - try the forum search feature and you should get plenty of opinions.
I forget the specifics but he fridge manufacturers provide the number of degrees that the fridge can be off level - you can convert that into inches based on the size of your rig. When I did the calculation it became obvious that in my rig anything that I would consider comfortable to camp in would be well within the limits of the fridge. After than I stopped being overly concerned about being "level".