Is there a way (supported/unsupported or even in theory) that I can create a calendar on my desktop via Thunderbird's lightning extension then sync that calendar file with Ubuntu One and then sync that same file on my Android phone in a way that the calendar application on it can update the file (and sync it back to the Ubuntu One cloud).
While I can't offer a solution concerning Ubuntu One, I can offer an alternative:
It's unbelievably easy to install, use and configure. Additionally, it offers fully functional synchronization for many online calendar services, e.g. Google Calendar.
I'm using it since ms windows times and it never failed me. I'm using it to sync my android phone and ubuntu calendars every day. It's the best calendar application out there IMHO.