There's lot of possibilities there; the demo page returns a tmp url that will work for a while with the data transfered, so you could use the service to distribute files in parts of 30MB max...
Yes, anyone can use your site to host any file on your server.
It's still interesting to explore the concept and think about how its always easier to build stuff exclusively client-side.
I think that's a flawed assertion. It's easy to make an insecure file upload in most server-side web languages. An example in the PHP manual is only a couple of lines of code:
http://www.php.net/manual/en/features.file-upload.post-metho...
How easy is it to make a safe client-side solution?
Do not do this.