Compromised phishing host notification

Hi all,

I had a question about notifying the owners of a site that appears to
be compromised and hosting a phishing page.  For instance, I received
a phishing mail today which linked to something like
http://www.domain.com/.www.creditunion.com/login.php
where www.domain.com was a small business here in the US.

Are there any common guidelines to notify the domain owners in a
situation like this, assuming I wanted to send them a friendly notice
and have no further involvement?  Would there be any possible legal
issues from a casual email, and would this be an effective way to deal
with the site?
What about a service like CastleCorps PIRT? (http://www.castlecops.com/pirt)
Is this more effective?

Thanks,
Colin

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