Anectdotal, but a non-profit volunteer org that I work with (http://cramba.org) had someone scrape all the contact emails from the site and sign them up for some mailings from a cycling tour company (http://kickassroadtrips.com/), sent via Mailchimp.

I directly reported this to Mailchimp itself, and based on both the response I got from Mailchimp and the angry response from the company owner I got a great feeling that Mailchimp took the abuse report quite seriously.