Thing #17 is Medium is the message, Prezi and slideshare.
I love Prezi, I played last year and made some quite slick productions for a few minutes of play, I have found other uses and had much fun since then too. Also had friends share their prezis and other information all of which I would have no idea with out this thing :-). Slideshare from what I have seen is more like a powerpoint and business tool, the market is much more traditional and is a very slick way to make and show information across many systems and means the finished item is what every one sees, and not as powerpoint which can sometimes reformat if the end user dosen't have microsoft office. I have browsed slide share and watched many different presentations, which have told me loads.
Prezi mean while is more the play side of presentations. I like Prezi, you can drag and twist, make funky or tone down, increase speed or freeze it, add moving pictures and anything else you have in your computer. Its fun and you can make rubbish and still learn through it. Of the two prezi is the one I would turn to to make some fun of my kids, or to show off some plan I had, while slide share is more a report format, calm and infomation heavy. But both are good tools for use.