What does the company do well? I think they do most things well... but you have to love that they offer their software free until you reach 2,000 contacts. They also make it very easy to create automated emails. The RSS to email feature is easy to set up and allows you to send your blog newsletter on a daily, weekly, or monthly basis at the same time each delivery.
What does the company not do well? Mailchimp is a little light on support. If you sign up for their free starter plan you will not receive any support... which seems fair. But even when you are a paying client they only offer email support and that is only after you have sufficiently searched for the answer in their help pages.
What do you wish you had known about the company before using? Take the extra time to verify your email and website.