Depends on the size of the presentations. If they're within the HTTP upload constraints of the server I'd be tempted to use a HTML form (the same way that BH uploads attachments). Using a log-on you could then have their uploads directed to their folder, and prevent them from viewing others' stuff.
Owncloud with a user account for each speaker?
I was going to go down the Owncloud route but I've ended up with a simple HTTP/PHP uploader.
No user accounts, just the upload folder being password protected.
And I stupidly forgot to change the PHP settings and all the files were too big. It meant the client was freaking out to my friend, so he was pestering me.
Ended up with a different uploader with a progress bar so people uploading massive files can see that uploading massive files takes ages.
Another example where doing a favour isn't worth it.
Out of interest, how much would someone here charge for what I've put together?
Simple webpage with PHP uploader including progress tracker (not made by me but taken an example online and used it). Hosted on my dedicated server, and there's so far been 2.2GB of uploads. FTP access to get what's been uploaded.