I tried to upgrade my system (wanted to), but the option was not available. Instead I was offered to install side by side or replace my current system. Is it not possible to use the upgrade method if multiple systems are detected (if not - shall I report a bug?)
I think that is a bug. I just installed Ubuntu Natty beta 2 today evening on my laptop which dual boots maverick and windows 7. I did the installation using the live CD and was given the option to upgrade leaving personal files intact.
However I did a clean install just to get a fresh start.