As my man MC_Van pointed out, what we're seeing on this end is that the MailChimp 1.2.5 plugin is adding an additional "Settings" link to all plugins. So, this means that if a plugin doesn't have a settings link originally, we'll add one that links to the MailChimp settings. Obviously not ideal, but it's something that will DEFINITELY be addressed in the next version that comes out.
From what we've seen thus far, when the MailChimp plugin is deactivated, those extra settings links go away. So, if a plugin is missing a "Settings" link after deactivating MailChimp 1.2.5, that should mean that the plugin didn't have any sort of settings link to begin with. Of course, if you do notice something weird, give us a shout back and we'll see if there is any specific behavior that we can replicate.
As far as the NextGen gallery, we haven't been able to replicate that specific issue. Here's a screenshot of our setup of NextGen and MailChimp activated:
Give us a shout if we can help with anything else!