You're right, BTLD, it's not very common to see very large tanks, especially in this economy at the moment.
I've had tanks up to 240g, and I've taken care of tanks all the way up to 280g. Personally, I enjoy smaller tanks, 125g or less. They are easier to reach all the spots, they are easier for water quality control, they are easier to clean algae off the entire glass. They are cost efficient, depending on your equipment - and they are easier to buy equipment for. It's also better to have a good looking tank filled with lots of corals that are growing out well into colonies than to have the same amount of coral in a larger tank that doesn't look full at all. Larger tanks take a whole lot longer to grow out - and the cost of keeping Ca and alk and magnesium up can be intimidating.