As a user who had no idea what he was about to read, here were my thoughts:
* The tagline below the logo is nearly perfect. Instantly told me what I was looking at.
* Gorgeous design. Love how simple the top section is.
* Plans & Pricing seems too prominent. I know you want me to click there so I can sign up, but ALL I know about the product is what I can guess from the tagline. I think you could remove it entirely (and make the "Next" button in the tour more prominent).
* I didn't really understand what was happening in the "Editing" screenshot. I wished the elements in the shot were labeled somehow.
* When I reached the "Viewing" screenshot, I only knew a change was made because I remembered the original tagline from a previous visit to Umbrella Today. I'm not sure it's clear otherwise.
* Plans & Pricing is gorgeous.
After that, I read the blog post, which gave me a much better overall picture of the product. It's written very well, though I'll admit raising an eyebrow at: "at this point, do you try to explain that your master branch has features that aren’t ready to go live yet?" This feels a little contrived. I think most folks know not to write long-running features in master, and I have little doubt that's how you're doing it at thoughtbot.
Just one guy's thoughts, though I am pretty squarely in your target market.
Anyhow, I'm psyched to see you guys launch this. It's clear you're scratching your own itch, and that's quite promising.