This indeed is a very interesting, and informative, discussion, so let me add my 2 cents to it...

Unfortunately, goldfish are still seen as cheap and easily disposable fish, and therefore for many people it doesn't make sense to buy a "cheap" fish and invest into a big tank for it (I do get the idea of a rubbermaid not neccessarily be an appealing object in your living room...

) Nobody would think of sticking an oscar, a cichlid, or a huge flowerhorn into a bowl or any kind of small container and expect it to grow big and healthy. Too bad that people's opinion of goldfish are the way they are, because those same oscar or flowerhorn keepers invest quite a load to keep their fish in proper shape, and hardly ever question the general rule of at least 50 gl for the fish.
So, why is it so hard to understand for people that goldfish are just the same? I always find it positive that Petsmart has started to mention 20 gl as standard for the fish, yet in the same sentence they lable it as a beginner fish, which in my opinion it is not.
As with any hobby, beginner goldfish keeper might start out in a bowl, evntually learn the right way to do it, and over time evolve into experience and the knowledge of how to proper care for their fish. I was the same - at one point having 12 big goldfish in a 55 gl tank. Not proud of it, no, but I am sure I have quite a huge number of people in my shoes. But you live and learn, and you change what you can.
Now, none of my fish, not even my tiniest telescope of barely 1 inch, has any less than 20 gl. Most of my fish, especially the bigger ones, have
at least 30 gl, even more than that for my single tailed comets and shubunkin. My 3 shubunkin are in a 160 gl tub, and believe me, they need every inch of it too. Quite a few experienced friends of mine with goldfish, they all have 50 gl per fish, but of course, those are mostly pond fish. It is kind of hard to envision the same gallonage for a tank fish. He might look quite lonely to an untrained eye. I had my big 9 inch oranda in a 29 gl tank during his quarantine period, and the poor thing had no problem at all filling that tank out. He actually was pretty happy when he joined the other orandas outside in their huge tub.
I think one of the main problems is that most people never get to see how much potential a goldfish really has. All they see are the tiny feeder fish, or just generally small fish, in a pet store. "How on earth can such a small fish need so much tank space?" - a very common thought, I am sure. Thats why I brought two of my largest adults to my daughter's school fair, when I heard that a parent gave away 300 feeder fish as prizes for games. You should have seen the parents' eyes when they realized how big their prize is gonna get! Shock, to say the least! Most parents thought that my adults were some kind of deformed oscar...
One other thing - the theory of "I buy a bigger setup once my fish starts growing" backfires a lot of times! Not only is there a whole lot more of work involved in form of tank maintenance with a smaller tank, the fish also will have some percentage of stunting already in him, and no matter how many times you "upgrade", the fish will always lack behind in his potential growing. Quite a big investment over time - in equipment that keeps piling up, but also in extra maintenance and time.
So, you save some in the initial tank setup, but you spend a whole lot of unneccessary money while "upgrading" every 6 months or so. Plus you risk your fish never seeing their true potential in growth, but they also will be exposed to a lot more stress in their small environment. Stress = illness, and here we go for medicine investments and such again. My fish hardly ever get sick, and there otta be a reason for that.
One last thought - very few people consider buying a Great Dane when they only live in a small apartment, or a huge sulcata tortoise if they don't have a backyard, or a trailer to haul that thing off to the vet. So, why is it that people find it perfectly fine to stick that potentially georgous and huge goldfish, yet small but still, into a tiny bowl, or even in some cases a 10 gl tank. If you ever saw an 8 inch fish in a 10 gl tank, you never look at goldfish the same way again, believe me.
Okay, now I am done, and I hope nobody is asleep yet
Sandtiger, as for those growth hormones supposedly not existing, go and visit a koi/goldfish show sometimes, and try to convince those koi keepers about that. Quite interesting actually to hear otherwise, that is something I never knew before either.
http://www.kokosgoldfish.invisionzone.com/...?showtopic=7981 I have talked to quite a lot of koi, and goldfish keepers, about that, and it was amazing what I heard. Yes, they are being taken out by water changes, but lets just guess how many beginners actually do a big weekly water change? Yeah, right, not that many. "Just topping off the water, or cleaning out once a month", thats what we get to hear.
I perfectly agree with more water for fish, no matter what size, but its a matter of believing, compared to the matter of people getting convinced. Lets face it, most learning occurs when people have to do it the hard way.