The latest flash 10 beta fixes the issue with youtube.
A good reason to move to flash 10 is that flash 9 can not load properly more than ~10 videos with sound.
Great script otherwise, though it'd be nice to be able to replace the player(but that's not exactly easy)

configuration does not work here(no errors, just nothing happens), everything else seems fine though.

Hum. I tried the testcase of the bug posted, but it worked here. Could it be more of an issue of cross-site httprequest maybe?

This script is not working here with firefox 3 nightlies/b3. It simply keeps on showing the "Loading flowplayer" text&icon and never goes beyond that. Note: I tried with a clean profile and it did the same.

Any chance you could do something like auto-load but not auto-play? Or is youtube not allowing that?(Another nice thing would be to add the ability to change the player to some of the free players around like flowplayer)