Many online video sites such as Youtube, Google Video, Dailymotion, Metacafe, and others only provide limited or inconvenient access to the videos; either they require you to install the proprietary Flash player (and I surely won't do that), and/or you can only view them online (but not download them).
There are some solutions, each with advantages and disadvantages:
After the download, you can either view the videos using (e.g.) mplayer, or recode them into a more sane format. For all of the above programs there are Debian packages available, except for VideoDownloader/UnPlug (but you can easily install those from within Firefox).
Update 2007-07-26: Added UnPlug and swfdec (thanks Joe Buck and Josh Triplet for the comments).
SELINUX=enforcing" to "
/etc/selinux/config(at least for now), otherwise my system won't boot up anymore because of SELinux denied permissions (I think). I'm pretty sure this is either a bug or me doing something wrong, but I haven't figured out yet what that is.