There is a difference between the client (which is proprietary), and the web
service (remember that the software is running on the server, and not your
computer, so it cannot do any harm. The only problem can be if the website is
using some JavaScript code with unmarked/non-free license, but that's a
freedom issue, and not a technical one, since the code is human-readable, so
it's safe to use it).
The reason to choose Ubuntu One for multimedia hosting is simple: it supports
embedding (and the video does not need to be re-encoded, 'cause that
automaticaly means lower quality, while doesn't give any benefits other than
HTML5 compatibility, which is anyway questionable, since the original
material is coded with Theora/Vorbis, which is already supported within
Firefox/Abrowser). I tinkered with various other options (Amazon S3, Dropbox,
FileChum, Google Drive, MediaFire, gobblin.se, Mega, and probably others),
but none of them worked the way I wanted, since the idea was to have it
playable within the Trisquel website.
MediaGoblin is great, except that it's working on a different principle (it a
web-player, with its usual side-effects), and cannot be used as a file
hosting service (this is not entirely true, since the uploaded media can be
downloaded in the originally uploaded source version, but embedding still
doesn't work).
