This Scientific American article says maybe cats purr not because they are happy, but as a way to communicate or do some self healing.
My cats purr when they think they are going to be fed, which isn't often enough for them. Here are some old pictures of our cats on Flickr.com.
I finished Pattern 5 of the Lace Sampler last night. I'll scan it and find something in the book that talks about it, then share.