Just for the record...ANY piercing can "grow out", get refused by the body, and rejected. It is not limited to just eyebrows, and, to my knowledge, eyebrows are no more susceptible than any other piercing. Rejections are usually a sign of something in the body...not the piercing, unless the piercing either wasn't clean or wasn't done properly.
The biggest problem I have had with my own eyebrow piercing(which I eventually removed because of this problem), and some of the hundreds that I have done for others, was getting the thing caught on shirts and tangled in hair, and having it pull and strectch. It hurts, it bleeds, and eventually the hole will heal too large for the current jewelry...but that is completely different than being rejected or "growing out". Also, the location at the brow tends to collect sweat, and can be more prone to infection, if a person isn't as "hygenic" as they should be. Where it is usually done is exactly where sweat is supposed to drip to in order to avoid it getting into your eyes(gotta love evolution), and so the sweat can buildup around the jewelry, leaving salt and oil deposits, and causing chronic infections.
Nomed-you are allergic to metal, but have you tried implant-grade surgical stainless steel? It is completely hypoallergenic, and even the most infection-susceptible people I have known can wear it, when all other metals cause infections. It is the thing I used the most for cartilege piercings(always susceptible to infection), and anyone who mentioned infections in previous piercings. It's a little more expensive, but worth it if you really want a cartilege piercing or are prone to infections or allergic reactions.
My ex could not wear any sort of earring, including 24K gold, because of chronic infections and an allergic reaction to most metals. She was so susceptible to infection that even Lexan(acrylics) jewelry caused her issues. It took me a year of convincing, but she finally allowed me to peirce her ears using implant-grade hoops, and she has worn them for 5 years with no issues. We even managed to get a belly ring to take using IGSS, though she took it out when she got pregnant with my daughter...