Email Newsletter Integration

I have read all the forums, etc about including email newsletter integration such as Mailchimp onto users' sites. I thought i had my question answered earlier when a rep told me that the Mailchimp would allow email optin through all of my users sites.

However, this is not the case. Now I need to find the best solution to be able to offer my users email newsletter optin integration. Does the general mailchimp work across multisite? Is there a plugin offered here? Are you guys working on one?

If not, what is the best solution you've seen thus far at making this possible for users of a multisite?

Thanks ,
Brian