[cabalamat]

I find Markdown best for writing in but looking at the processed output best for proofreading.

[filmgirlcw]

This. I've been making my living as a writer for ~7 years and have used Markdown as my dominant syntax for about 6.5 of those years. When I proofread, especially a long post, a preview is great.

Of course, for that, I usually just use Marked, but I'm never opposed to seeing more Markdown tools. Ever.