OK, revision time. AFAIK from this thread: 1. there is no problem with the hardware or the alsa driver, as sound, in general works.
2. the problem is in flash video (you mentioned youtube). What we don't know is which browser you are using, which flash plugin, nor whether other media works in the browser (eg those requiring mplayerplug-in, realplayer etc). 3. I come back to my earlier comment that my recollection is that the flash plugin uses OSS, the deprecated predecessor to alsa. Alsa has an OSS emulation layer and we have established that you have the appropriate driver installed for that. However i would now check the permissions on /dev/dsp (and if that is a link to something else then the permissions on the link's destination. Make sure you are in the group that owns the device (or if it is a link the link's destination) [1]. Don't forget that after adding yourself to a group you must log out and log back in again for it to take effect. 4. If you also have the problem in mplayerplug-in, I suggest setting it to use alsa in /etc/mplayerplug-in.conf (set ao=alsa).
