I made an IPA...added approx. 3 oz of apricot extract to the keg and transferred on top of it. Force carbed it and a few days later, tasted pretty good, but still "green". A month later, bottled a few and took over to my LHBS, got a couple of compliments on it...one even said it seemed very close to Magic Hat #9 (which was my goal). If I do it again, I'll scale back to 2 oz, it is a little stronger than I wanted.
I tasted the extract straight from the container and it is so concentrated that I would definitely categorize it as medicinal. I could easily see that too much could cause an off/unexpected taste. For what it's worth, my extract was produced by LD Carlson..no idea that makes a difference. My first experience with a fruit extract, it wasn't a bad one, but now I'm a little hesitant to try another. I'd like to try a fruit/wheat for the summer, maybe I'll try actual fruit or puree as described above....doing it this way would make it more "my beer" rather than a flavor created in a lab.
As with any batch gone bad...please accept my condolences.