Out of all the email broadcast services that serve the SMB market, MailChimp is #1. Here's one unscientific measure from new web app directory Best Vendor, and something more reliable from Google Trends.
Generally, MailChimp's stature is deserved. One of my clients uses them for a regular newsletter, and we're all happy.
But any market leader needs antagonists at their heels, or they become fat and unresponsive to customers.
Which is why I was glad to see Campaign Monitor add an RSS-to-email feature last week. MailChimp has had this feature for a long time, and Feedburner for even longer. This new feature is a bit hobbled with the absence of dynamic subject lines, but we should expcet that to come soon.
I have long admired the Campaign Monitor user interface -- which IMHO is still preferable to MailChimp's -- and it's reassuring to see them continue to develop their product.
MailChimp will probably never look like Ma Bell, but healthy competition means that outcome is even more unlikely.