Many species have been saved from extinction by captive breeding. Examples include:
Guam rails (bred by Division of Aquatic and Wildlife Resources and some US zoos)
black-footed ferrets (bred by USF&W)
California condors (Bred at San Diego Zoo and Los Angeles Zoo)
Przewalski’s horses (saved by zoos coordinated by Foundation for the Preservation and Protection of the Przewalski's horse)
scimitar-horned oryx (hasn't been seen in the wild in 15 years. Lives "wild" in fenced areas. I don't think I'd call this hobbyist effort, either)
Partula snails (scientists studying the Genus and the Zoological Society of London)
Spix’s macaws (conservation groups organized under the Brazilian government)
From "Herpetoculture and Conservation":
" It seems too many herpetoculturists use conservation to promote their own interests. As Dodd (1987) wrote: "Too many propagation programs are operated under the guise of 'conservation.' When this really means to supply individuals with a sufficient number of pets, this is not conservation but recreational use of wildlife." That doesn't mean that herpetoculturists cannot be conservationists, but private herpetoculture is not (or should not be) a conservation tool. Herpetoculturists can promote conservation in many ways, including:
Stop collecting wild animals and purchase only captive born animals. By purchasing only captive born animals you will not be directly supporting the collection of wild animals. In addition, you'll generally get healthier animals. All in all, captive born animals are a much better buy.
Encourage others to buy captive born animals. As herpetoculturists, we are often asked to talk to groups about amphibians and reptiles. Invariably, someone is interested in getting a herp as a pet and asks where they can get one. We should tell the group that we only keep captive born animals. This may seem odd, but remember the people you are talking to can't tell if the animal you are holding is wild caught. If the person does get a captive born animal they are more likely to have a good experience and want to continue keeping herps.
Obey local, state, and federal laws when both keeping (and collecting, if you must) herps. Unfortunately, many of our headaches today are caused by a few money hungry herpers who think they are above the law. The result of their greedy actions are stricter laws which ultimately encourage more people to break the law (and the cycle continues).
If you must collect, do it in an environmentally safe manner. First of all, you should question why you must collect these animals. Are your reasons valid? When collecting, replace, to the best of your ability, everything you move.
Keep quite about good herpin' sites. All too often herpetologists tell their friends about good herpin' sites, who tell their friends, who tell their friends...and eventually everyone knows about the area. Soon the area becomes a not-so-good herpin' area.
Do not release animals that have been in captivity, including newborns. The risk of introducing disease or detrimental genetic components is too high. This includes animals that were kept for a couple of months. It would be better to donate the animal to a museum (with collection data) than release it. Only consider releasing an animal that has been kept for less than two weeks and has been maintained in quarantine.
Finally, if you really want to contribute to conservation efforts, donate a portion of your herpetoculture profits to an established conservation group that has herpetological projects. What better way to justify our hobby?
http://www.anapsid.org/conserv.html
Just think about what you guys are REALLY doing. When have any other species you've imported generated this much division and heated feelings? Is it really worth it to make more pets?