I think corydoras are interesting in themselves and deserve better treatment. I've continually seen bronze cories used as "cleaner fish" in local pet shops, with just one per tank, ranging from guppy tanks to African cichlid tanks. Lots of people see this and do the exact same thing at home. They are a shoaling fish and should be kept in groups; they like slightly soft acidic water. Because they're so hardy they are kept in some really extreme conditions. Also, people think that they can survive on uneaten food. While they most probably can because they're so hardy, it's like starvation and food should be put on the bottom for them. Tankmates should also be considered. I had Blue Rams in the same tank with 5 cories, the rams would eat all the food I'd put on the bottom (intended for the cats) until it became so bad I had to separate the two. Top dwellers, like zebras, Rainbows and most characins are fine tankmates. Finally, many people put cories in a Discus tank, but cories come from cooler temperatures and in most cases are never at their best in a Discus tank.
I keep 3 in my tank, and they all seem to be fine. The only major problem that I have is that whenever I feed my catfishes, my Guppies and Swordtails will come and nip at them, so they can eat the pellets for the catfishes! Other than that, they are really good fishes.
I have 4 of them and 2 panda cories and the six of them always school together. One bronze is only 2 cm while the largest is 5 cm long. They still school together despite the difference of size and are very active, always swimming to the surface for a gulp of air. They are doing very well with tetras, clown loaches and platys in my 55 litre tank.
I have two corys and just wanted to comment that if they are continually shooting up to the surface it could be a sign of low oxygen. They can process air in their gut and mine were constantly darting up to gulp air when my pump broke and there was an oxygen shortage. Now that it's fixed, they occasionally go to the surface, but not much. They are great fish.
I always have some (3 to 6) Corydoras aeneus in my aquariums and I can say that they not only are excellent and peaceful fish for a comunity tank, they in fact contribute to the keep everything polished (except the algae on the glass). At least two comments referred that they donīt understand why cories go up to the surface. The answer is easy: they need to do it to survive, because they have an auxiliary respiratory system that uses the digestive system organs to help them do get more air, absorbed by the anal cavity. As they get older, they tend to do it less often, because the respiratory organs get larger and with higher capacity.
I have a pair of bronze cory's in my 100 L community tank. They are very playful with each other and at times appear to be wrestling. They seem to live in a world of their own and absolutely nothing appears to bother them, whether it be other fish or me with the syphon cleaning the tank. They are very hardy and are ideal for the beginner.