From what I've been able to discern, it's really meant to be filtered out before the beer is consumed. There are concerns about kidney blockage. Admittedly, at the amounts we use it seems unlikely to be a problem, but I have enough medical issues already that I'd just as soon limit its use as much as possible. I've pretty much stopped using it in the kettle, whereas previously I would add a fair amount to every boil. With a bit of vigilance I can control the boil with the valve and a spray bottle. I also don't add it to fermenters as a matter of course as I used to. If I can't control the fermentation some other way, I'll add the least amount I can get away with when I need it. PLease understand that I'm not trying to tell anybody what they should do. This is simply my own decision.
That is good information Denny. Why risk it if it a possibility? I am usually brewing only 5-10 gallon batches in a 15 gallon BK, so boilover is rarely an issue, but I have heard that Fermcap aids in head retention as well. I haven't seen any data regarding this, but the report comes from a reputable brewer that I trust.
With that being said, I really don't think awesome head retention is worth potential kidney issues such as blockage. At the end of the day, if the beer is good that is all that matters. If the beer is in competition, Appearance is only worth 3 points max, right?