I also agree, it's quite unique enough to stand on it's own, without necessarily defining it up front. Doing so pigeon-holes it actually, and into something it's either really not, or won't be 30 days from now. Even tho I had some idea (as detailed in my other reply I came for blogging), I still had to spend quite a bit of time here to wrap my head around what exactly Steemit is. And it's already different from what is was once I thought I'd figured it out! It's so many things in one, and the launchpad to many other apps thanks to all the developers here. The state of constant evolution and testing seems to make it harder and more pointless to define summarily in fact.
"Steemit - the new way to Internet..." or maybe "Steemit - come evolve with us"