I use MailChim Sync for one of the sites on my Multisite. This plugins would be actually a way more usefull if it was possible to enable it on a Per-Site-Basis. Why am I suggesting this?
Then, each Child-Site could have its own MailChimp List Synced (when Per-Site-Enabled) or a single MailChimp List Synced for the whole Multisite (when Network-Enabled).
I feel that the plugin could be exponentially better this way (multiply it for each Child-Site of each Multisite on the whole planet)... Hope our Super-Heores can handle that!