For example, if I'm sending a "Here's your password reset email" via MailChimp, will I now have to worry about it not just potentially going into spam, but also under some tab that the user may not look.
I'm only really concerned about the transactional email, whilst we send list mail too I think it's reasonable that is classified however the user and the user client deems fit (if they wish to receive that at all). But when it comes to an email that the user has explicitly requested and expects immediately, not having it go straight to their visible and main inbox is an issue.