I did not specifiy the driver level in the subject line b/c it doesn't seem to mater.. I have tried the Ubuntu 8.10 default nvidia driver (177.80).. I have upgraded to 177.82 by hand (the latest stable), and have tried 180.11 and 180.16, which have caused or at least coincided with massive system instability, and have been unable to install 180.18. But the results I got with 180.11 and 16 were appreciably the same as with 177.8x
here is what I did...
A (no nvidia driver)
-fresh new install of Ubuntu 8.10.. via wubi, 32-bit... reboot to using NO nvidia driver (as default) and a screen rez of 1280x800
-launch synaptic, add in the additional repositories.. install flashplugin-nonfree 10.0.15.3ubuntu1.
-launch Firefox and go to youtube link.. normal size plays fine... full screen (1280x800) plays without any obvious stutter.
-install Intrepid-level nvidia restricted driver (177.80 per the nvidia settings panel) via System->Hardware Drivers and reboot (to glorious 1080p) to activate new driver
-launch Firefox and go to youtube link.. at this point even the normal size is a tad jerky, and full screen is the same lost cause as I've been seeing in my previous installs.
- I go to the screen resolution panel and drop to 1280x720 (to compare against the no-nvidia screen res and its still jerky.
At this point I have not upgraded/installed _anything_ else... so I don't think it can be a driver conflict, and given the Flash perfornace before installing the nvidia driver, I'm not inclined to blame the Flash plugin, at least not by itself...
Again, I realize it would be much better to be running the most current dirver and debug against that, but as I said, I did try several 180.x drivers briefly and saw no improvement, but I also got many system lockups so I would like to stick with 177 until there is a compelling reason to switch. From what I saw with 180.xx no improvements were made to the code in this area.
I have an Acer AX1200, 2.7 Ghz dual-core, 3G ram, on-board geForce 8200
EDIT: I have also applied the performance tweaks from http://www.nvnews.net/vbulletin/showthread.php?t=118088
with no visible improvement (with regard to Flash)