OK,
Sorry for the delay.
I had trouble finding the original source of where I read Heiko Bleher's views on rainbows being brackish (celebes are different, so these comments don't necessarily apply to them), so I PM'd him on a rainbowfish site and this is his entire response word for word:
"Hi,
just a fast answer to your question: rainbowfishes are NOT used to brackish water - none. Only some species of blue eyes are.
Do NOT keep rainbowfishes in brackish watrer and do not try it, if you love your fishes. And why should you? The boesemani live in a pure freshwater lake in the center of the Vogelkop peninsula in New Guinea and have NO access to saltwater whatsoever.
If you want to be good with your fishes and enjoy them, dont. If you want to follow other, who have no idea and never went to colelct and never researched the habitats (as I do all the time), than just do it. It is up to you.
All the best
Heiko"
Like I said, he's certain about his answer, and he's got more field research experience than any other human alive, but If you don't just want to trust one source even though he's the most famous and generally accepted as the most knowledgeable person on the subject, here's a thread where other rainbowfish afficionados visit the subject:
http://bowheads.org/forums/showthread.php?t=1707&highlight=brackish "Rainbowfish" is Gary Lange's handle, he's the rainbow expert in the US, gives talks regularly, and currently keeps about 30 species of rainbows. "Coralnerd" who referenced the article that found that long term exposure to salt reduced longevity, is a marine biologist who also keeps several rainbow species, but mostly Australian species. It should also be noted that the Australian species used in the article are some of the more salt-tolerant rainbows. Bosemanis, praecox, lacustrus, herbertaxelrodis, and incisus are all more common in pet shops, but are all PNG species that live in tropical jungle lakes or streams, have no access to saltwater, never experience high salt conditions in the wild, and therefore have an even lower salt tolerance than the Australian species.
Those are my sources, what are yours?