[exim] Exim and SPF

Is anyone using SPF in Exim? I'm still trying to figure out a use for it.

One thing I thought of is a way of determining who is forwarding email.
If SPF doesn't match but the email is clearly not spam then the sending
host might be forwarding email and might make it on a list of legit
forwarders.

Might be a way of detecting spammers who use SPF by the hosts they
reference in their SPF record.

I might send out notices to those with too restrictive of SPF that their
email might bounce if the recipient uses hosted spam filtering.

What are the rest of you doing with SPF?