Aha, let me issue a correction, now. The problem is indeed resolved in 12.04.
I shall now uselessly provide the entire tale:
Basically, my 12.04 upgrade didn't work properly, failing out initially due to a download problem. I restarted the upgrade later and it seemed to work mostly okay, but I did show a few errors (mostly things already being installed and configured, which I presumed was not anything to worry about).
But, I did still have an issue with a lot of widgets in my panel not being found, so I attempted to sudo apt-get install kdeplasma-addons, but that wouldn't work, so I had to do sudo apt-get -f install . . . which seemed to resolve the remaining flaws in 12.04, I thought.
It was under that state that I posted last, after having done some testing with the acpi_backlight=vendor setting. But it didn't work, as noted, so I put it back to the way it was (with vendor, so I had brightness control).
Today, however, I was informed that I had 4 security updates and 941 program updates, which seemed rather odd to me given the presumably-successful upgrade. So I attempted the updates but they failed three times (freezing in mid-update), requiring sudo dpkg --configure -a to clear it each time and start anew.
Now, finally, I believed 12.04's update to be complete. I had a new Grub2 entry indicating a new kernel and all, which had been the same before. But then I kept having a weird issue where my laptop would power itself off after like a minute sometimes (when not watching a video). I could wake it up (so it was sleeping), but it was annoying, and seemed to indicate something was amiss.
Then it finally hit me . . . during the testing, I'd set it to go to sleep after a minute when on battery power. It wasn't a new problem . . . the bloody thing finally was working!
So, apparently the new kernel with 12.04 provides some assistance in that regard, though for the record I am still using acpi_backlight=vendor.
If anyone is having issues still, please advise. I'll monitor the thread and we can go over any settings. I'm no expert, but it is working on mine, so there ya go.