My adventures in being stupid.
Of course I had to try this myself. Had Helena KDE CE final running on a 6 year old (upgraded) HP a645c: AMD 3200+/1.0Gb memory/Nvidia XFX 6200/256Mb dedicated/200Gb HDD (65Gb linux partition). Ran just fine on the original install. Stable and fast.
Used the terminal and Kstorm's way of upgrading. Upgrade process went okay.
First reboot initially came up with the new login screen which stayed there for about 2 seconds then 3 evenly spaced, multi-colored squares appeared across the screen near the top and the whole screen went blank. My display warned me it had lost the signal.
On a hunch I typed my password and hit enter. The hard rive crunched away and eventually the login music started playing so I had apparently made it to the desktop although I couldn't see it.
I held the power button in which turned off the computer, powered it back on and let it boot back into Mint. This time when the login screen came up I immediately began typing in my password. The login screen didn't disappear this time. Apparently the act of typing prevented the graphic corruption of the login screen from taking place.
>Logging out and back in doesn't exhibit the login screen blackout, only restarting or a fresh boot from power up.
>I eventually found that hitting CTRL+ALT+F1 and then CTRL+ALT+F7 brings back the login screen if it disappears on boot.
Initially there was a lot of GUI breakup in the desktop including deterioration in the panel (part of it blacked out) and rather large black squares adorning the bottom left of any notification box or app thumbnail generated by the panel (mouse hover, etc). I went to System Settings/Desktop (left sidebar in "Desktop" took several seconds to appear, BTW) and disabled Desktop Effects. That got rid of the panel anomalies. I then re-enabled Desktop effects and the panel has been fine since. The panel really has problems if I leave desktop effects disabled. Don't know why.
After all the above I did a few logouts and logins with no problems but reboots still came up with the disappearing login screen. I would think that just hitting CTRL+ALT+F7 would bring it back but I haven't tried that yet (getting late in my part of the world).
Overall, KDE 4.4 is still usable and actually appears to be a bit snappier than 4.3.5. But there are definitely glitches in the GUI rendering where 4.3.5 was rock stable with no problems whatsoever.
Of course the question is now, do we leave the Kubuntu backports enabled in Software Sources in hopes of eventual fixes to 4.4 down the line or should we just say; 'Well, wasn't that fun?" and start from scratch with a reload of Mint 8 KDE CE?
"Humph. Choice, it is the quintessential Linux delusion, simultaneously the source of it's greatest strength, and it's greatest weakness." (All apologies to The Architect)