Is in progress on my main desktop box. About 20 minutes to go on the package download.
I'm posting this from an older box that is already running Natty using LXDE for the GUI environment.
Updates to follow:
Quick updates update from almost a month out. The package download did end up taking about 20 minutes. I don't have an accurate time on how long it took to install the new packages. I walked away after about ten minutes when I returned there was a dialog window open asking if I wanted to keep my existing CUPS configuration. I don't know how long the process had been waiting on me to answer that question. With my ten minute absence it took around 30 minutes; previous dist-upgrades have taken as long as ninety minutes.
Upon reboot I logged in to Unity. I have to say I just don't get it. I found some tips and tricks online that helped learning how to use it; changing my mouse focus to click to focus made the top bar (name check) usable, the desktop switcher is pretty much useless if one can do everything it does with keyboard shortcuts, then there are the freezes. So I switched to Classic and still had the freezes or lockups.
Overall the dist-upgrade process was painless. I'm not sure I like where Ubuntu is heading with Gnome.