Me too, totally frustrating, one day its ok and the next nothing -
Google should be helping us here as I have adsense on my email!! Have
been reading about MailChimp so decided to have a go at setting up
email subs with them - however, when choosing an option to use my RSS
feed to send out posts on email with MailChimp, it didn't work. I set
one up as a 'campaign' which requires you to manually complete your
email that you want to send out, and it an email was sent. So, I do
think its an inherent problem with Feedburner/RSS for some of us at
least!