SSLMate founder Andrew Ayer has posted on his blog about his experience using SSLMate auto-renewal with one of his website's certificates:

Yesterday I renewed the about-to-expire SSL certificate for one of my websites. I did so without running a single command, filling out a single form, taking out my credit card, or even logging into any server. All I did was open a link in an email and click a single button. Soon after, my website was serving a renewed certificate to visitors.

The blog post also drops a hint about SSLMate's upcoming import feature - soon you'll be able to use SSLMate to manage not only certificates purchased through SSLMate, but certificates you've purchased from other vendors as well. Stay tuned for an announcement!