This is an old post but since someone bumped it, I'll add don't forget about children's daycare centers. I am a teacher in daycare, and we use acrylic and cotton yarn A LOT for arts and crafts. The owners would never buy something like that so we have to depend on donations, or bring in our own if we run out.
I think seniors would appreciate it the most. They need to maintain an active lifestyle, not just for the body, but for the mind as well. Knitting, crocheting, and arts/crafts help keep their minds active and creative.