At the moment its possible to download the orginal high quaility version of any clip you want for free simply by looking at what video number your watching and then going to http://www.thesite.com/video/69.avi (or.wmv, .mpg etc) so there would need to be some protections to stop anyone getting the files and so that users cant share the download links with everyone.
You can prevent this by using .htaccess file.

deny from all

As for the download feature, we will see what can be done once the current bug fixes are finished.

I don't think payment based packages will work unless you got some special content, now with lot of video sites, people have other choices.