As for the power button long press, i held it down for a couple of seconds, then on release the screen would light up and give me a "press fullscreen to unlock" message.
After adding the CSSU to the 800 and rebooting, ASUI is back to its normal behaviour... sorry for the corner case
I did spot another niggling detail though (probably nothing to do with ASUI) : on the 800, in Cpanel/Navigation, I can uncheck the standard Maemo battery icon, and check the ASUI one in its place. On the 810 I can't because the Maemo icon is greyed out (and checked), so I'd end up with two. Strange.
sed -i "s:^Mandatory=true$:#Mandatory=true:g" /usr/share/applications/hildon-status-bar/hildon-status-bar-battery.desktop