I tried the application, and it looks great!

One thing Caret gets right that other Markdown editors (Macdown is what I currently use) don't is wordcount. In Caret, the document wordcount is always visible in the upper right corner, and if I select some text, the wordcount for the selection is displayed again. Others have mentioned the lack of live-preview as a deal-breaker, but I'm ok with this because of the easy, obvious shortcut. My main purpose with Markdown editors is writing READMEs and blog posts, and I usually don't keep live-preview open as I'm writing.

The one missing feature to keep me from pre-ordering is detection of jekyll YAML headers.