a 240 gallon high (6 foot, 32 inches high) tank at my lfs has quite a large chip in the bottom right side, and is not leaking, and it is about 20 years old. oh and by the way, a tank exactly the same size and the same age exploded (front glass gave way) a few months ago, an it was about 4 foot off the ground, and the 2 foot saratoga that was in it was on the floor. there is a large hole in the wooden floor from where a shard of glass went straight through the floor. apparently it had a similar chip in it but in the middle of the front glass, that started leaking a few hours before it 'exploded' (thats what the manager said happened)
oh and they were glass tanks