Something for uploading and making annotations on slides?
Why do I want to do that?
So however easy or un-punishing "it" is, is really irrelevant.
Re the problem we are trying to solve: giving feedback on documents really sucks. Emailing around 'Slide 1: change x,y,z, Slide 2: change this' and other out-of-context comments is a massive pain-point for users, who want to be able to do it quickly, visually, and in their browser (instead of in an old piece of desktop software). Feel free to ping me on leo@kivo.com if you have any more questions.
Also, common questions like "where are my documents stored", "is it secure", "how do I share the result and who can see it"... remain unanswered.
The only parts of the site that should be hidden behind the sign up process are those that only affect logged-in users; learning about the site and business is not one of those. Most of that information does not need to be located at the front page itself, but there must be a link allowing the user to find it.