I've always used baby powder to put bladders in place. Few times heard, that it is bad for bladders. Can someone confirm / confute this statement?
it's not bad at all for the bladders the problem is when you get a hole, and need to do a repair, the baby powder is all over the bladder, so if you just do a regular stick with tear air or a fix it valve, it will peel off. On a regular bladder, you can just use rubbing alcohol to clean, but on a bladder with baby powder I will always make sure to lightly sand the bladder before fixing a hole, it not only gets the powder off so your patch will stick, it also gives you a better mechanical adhesion -- which I guess is something you should do every repair, but it is especially important if a bladder has powder on it, make sure you sand it before a patch.
Short answer -- no it's not bad for the bladder, but it will mean when you do your next patch you have to make sure to get all the powder off so your patch will stick.