1) The advantage over the personal homepage is that more people will see it. Would a video get more views on your blog or on a video sharing site with lots of content where people went to find content like that? 2) I think the idea is that instead of using the current journal system, where professors try to show how their work has an impact for their university by paying to put it behind a paywall is just broken. Ideally professors will post straight to Academia and bypass publishers altogether. if you want people to read your work, putting it in an open, free forum where more people will see it AND you can track the metrics of your work seems far preferable to paying to put your work behind a paywall if you go the traditional route. I think they seem to acknowledge that publishers won't be pleased if you post your already published work on Academia. 3) The answer to the final thing seems to just be that it is a really tough technical challenge. They seem to be a fairly small team and the facebook motto that "the journey is 1% finished" seems to apply here. Imagine the possibilities if this takes off. We currently think of journals as paper with ink on the pages, but a site where all academics can share their work, and we see new ways of sharing research, like executable code, rich media, etc, could really improve academia and science in general IMO.