That is exactly what he did. Just because it's closed source doesn't mean it's fair to make an identical copy (in the interface and interaction design sense) that is free.
You have a social/emotional complaint: someone took your good idea (and kudos to you: it's a great idea!), and duplicated it. But it's recognized (and documented here) that you were the progenitor of the idea, and if you eventually open source the original, I can't see how this will "hurt" you. People have an innate sense of fairness, and duplicating ideas like this goes against it in a small way.
But it's not theft (or even copyright infringement), and by overreacting you are going to alienate people who would otherwise be sympathetic.
No, never, as long as the open-source alternative doesn't actually copy any copyrightable material from the original (such as images or other data). And I don't see any signs of that here.
On the contrary, creating an open-source alternative to closed-source software is considered awesome.
Not under any definition of "theft" in use outside IP troll offices, as far as I know.
Feel for you here dcurtis, and surprised people are actually behind this.
Plus, your value is not the app, it's the people in the network, so stay calm and let us not-so-cool people use the open-source clone.
In fact, you could assume the opposite: that, because he is a professional designer, it took him less time to design the app than it would've taken a "layman". (I'm not forgetting about the perfectionism of many designers, mind you)
You can't go around putting the Coke label on different fizzy beverages.
Svbtle is obviously popular for its brand. You are stealing its brand and using it for unintended purposes. The only value in what you've created is that it looks like Dustin's work.
Ripping that off wholesale diminishes the value of something Dustin work(ed/s) very hard to create and curate. Thousands of decisions went into that design. The design is a mark of quality.
Show some respect.
2. Brand? What brand? It's a blogging platform. People don't want it because of a brand. They want it because it's a good idea (simplistic blogging).
3. Coke has a trademarked label. This is merely a website. What is dustin going to trademark/copyright? The ratio of whitespace to small, grey lines?