Although the 9.0.124 version has been way more stable and reliable for me (running AMD64), it seems improvements are on their way in the updates:
Technorati Tags: ubuntu, hardy, flashplugin, updatesChangelog
flashplugin-nonfree (9.0.124.0ubuntu2) hardy; urgency=low
* fix "frequent crashes with flash on youtube"; we fix this by
demoting libflashsupport from depends: to suggests: (LP: #192888)
This has positive as well as negative consequences:
(+) increased stability for firefox and nspluginwrapper
(-) pulseaudio users reported that this breaks sound if flash
while other applications are running that use the sound
device for output.
Users that installed libflashsupport during hardy cycle should
uninstall it to increase stability.
- update debian/control

g post: