This is a url for Channel 4 in the UK. There is some regional blocking and I'm not quite in UK and can access it, so I'll say little. I have ATI cards, and have issues with flash movies and decided to try gnash, after exhausting the road with the adobe flash player. I've been testing using the videos (in series 12) as a test, as there is a speech usually at the start and the synch slips on speech. I put up screenshots of what I'm seeing on OSS drivers with gnash and adobe flash. In gnash I'm missing the play buttons.
I'll also mention packaging on Slackware, as you seem to have considered every other major package type. The Makefile supports $DESTDIR but throws horrible warnings. The usual routine on Slackware is is:
./configure <stuff> make make DESTDIR=/tmp/package install #this stage throws horrible warnings and dire threats. I did run the libtool command it roared at me to run.
cd /tmp/package # Add in fancy stuff line install scripts, information page, etc.
makepkg ../packagename/t?z #This throws a txz or tgz package
Then install & uninstall are painless with installpkg & removepkg.