The following is a post from basket_case from a thread whose subject is "2 questions pt2" from August 2011
Small Friend Pendant = +25% FP
Medium Friend Pendant = +50% FP
Large Friend Pendant = +100% FP
They work on villagers and sprites as far as I know; they do not work on animals.
With the Large Pendant equipped, you'd get 200 FP for talking and 600 FP for a small gift. The effects also add up if you have more than one equipped (but not stacked) even if they're the same Pendant -- which can be huge. With 3 Large Pendants and an 800 FP gift you would get 2400 FP. If you win a festival with them equipped you could get up to 3-4 times the FP with everyone present.
I've never bothered with the recovery earrings (except to obtain every accessory); I've never noticed them actually doing anything.
in another post it was mentioned that you can use 4 pendants unstacked.
That's where I got the information I posted. I have used three pendants and it worked on the Mineral Town people, who you only have about 25 days to raise their friendship points every year.