we're implementing the _dmarc record per default with all our (new) customers, gives us more information about where the email goes and if they are suffering from possible Phishing/Spoofing of domains.
We see in the Netherlands that banks are adopting DKIM/SPF and DMARC much faster to prevent/protect customers against phishing.
At this point XS4ALL is reporting, so if you implemented DMARC
According to ING (dutch bank) they lowered the amount of phishing messages. (Dutch article:
http://www.ing.nl/nieuws/nieuws_en_persberichten/2012/09/xs4all_en_ing_samen_valse_emails_te_lijf.aspx)
The DMARC reports tell you which IP is sending e-mail and pretending to be domain X, it also validates SPF and DKIM.
If you set the policy records you can advise what the ISP should do if they receive messages that fail the SPF or DKIM check.
The aggregated reports or authentication failed reports are nothing like Feedbackloop messages, so the only use for them is separate interpretation of your email/domain flows.