Im using the latest version of the plugin (v1.2.1) and have noticed lately some inconsistency with its function.
I have customized the look quite a bit with simple CSS. All aspects of the form work correctly in Safari. What I see is that occasionally (not always) the subscribe button is disabled on page load in FF and Chrome. I looked at mailchimp.js and it seems that maybe some browsers (Firefox) interpret the attribute disabled="" as meaning that the submit button should be disabled. Perhaps the better jQuery for enabling the button would be removeAttr to remove the disabled attribute altogether? On another note, the success message doesn't correctly populate in some browsers, regardless of success or error.
Has anyone else had problems like these?