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I am happy to see that this module now supports limited Rules integration, however the subscription action Subscribe user to a mailchimp list cannot be used for interacting with anonymous visitors. The action will only accept a numeric UserID so it cannot use an email address, for example, that was submitted by an anonymous user through a Webform or as part of a product purchase in an e-commerce setting. See the power of this?
I actually wrote a patch for this and realized that someone else had written a nearly identical patch inso I'm re-uploading that user's patch since they did it first.
Anyway, I've tested the patch and it works great.