There is a signaling effect from using Svbtle (Their aim is to signal "you are going to be reading good content") but it's hard to understand why you wouldn't want to use your own design and brand for your site. You are ceding control of your online brand to their design framework.
I humbly disagree: As a writer, I'd like my design handled for me. I just want to be able to write the best piece within reach & present it to the world in a way that will gain mass distribution.
Besides that, as a reader, it's easy to detect the Svbtle "look" & know that this article will probably be worth my time.
It's going off-topic, but this is something that has impressed me a lot in the growth of the network: by being part of Svbtle, that means you're leaving the design of your blog and your homepage to Dustin Curtis's design, besides a color and a logo.
That he managed to convince that many high-calibre people so fast is very impressive. (especially since they have better things to do than thinking about joining a blog network. Most of them don't need that at all)
It's fun to watch this thing develop.