Is nature causally closed?

Just got done reading Jason / immanent transcendence's post on the causal closure of nature.  Wow, what a great post.  Now, I follow his line of thinking - but beware, read slowly to follow it.  Some twists and turns and this turns out to be one of the more subtle posts you'll read in quite awhile.  It left me wondering more deeply about the topic, which is exactly the sort of thing that I enjoy to read.