At one time, I had a 20 gal community tank, a 45 gal So Amer cichlid tank and a 45 gal African cichlid tank going at the same time. I was a member of the aquarium society in Boston, and we'd often have meetings at the NE Aquarium. (There was also cross-over between that group and the homebrewers group in Boston as well).
When my kids were little we had a 30 in the living room with fresh water and a couple of different kinds of filters. One day I got up and went out in the living room to look at it and I was so surprised.....I didn't know that fish knew how to do the backstroke.
I had one when I was a kid, nothing fancy, just a goldfish in it.
For the past couple of years I have been trying to convince my woman that I need a large tank, and a hermit crab. I think they are the neatest things, I always played with them at the beach at my grandmothers as a kid.