I was running Debian and I wanted to try Ubuntu, but Ubuntu Desktop out-of-box doesn't support this kind of configuration. Ubuntu Server advertises LVM support, but for whatever reason didn't recognize my configuration. I probably could have recreated the same configuration w/ Ubuntu Server's installer, but I didn't want to risk losing my data and then discovering it doesn't actually support it.
Finally after some trial and error I figured out the Ubuntu Alternate distribution has LVM and software RAID support if you run it in "expert" mode. It was a bit of a pain to manually walk it through the installer, but eventually it recognized my existing drive configuration. Definitely not the "friendly" Ubuntu installation experience I was hoping for, but it worked.
When the install was done it left me with a console-only bare-bones install. But since I had the Ubuntu Desktop CD handy, I popped it in the drive and ran:
apt-get install ubuntu-desktop
...and away it went.