Had my interview...
they asked the same basic questions: do I have family in the US and UK, when did we meet, how did we meet, when did we meet in person, how long have we lived together, how did I support myself.
Then the specific questions came:
do we have any assets?
is the landlord happy with me staying there after the civil partnership?
how many passports do I have and do I have my last one?
They kept repeating some questions, mainly: How long do I intend to stay in the UK and how will I support myself before the civil partnership.
At the end they were 10 minutes late and the interview lasted 22 minutes. I did not get a decision (suprise!) because they were not satisfied with the bank statement I submitted last week which showed we were £400 into the overdraft. I will submit an updated one since my fiancée's former boss paid her the severance pay and we now have a significantly higher balance. I will also give them my old passport (since the ECO didn't ask for it last week! I guess they don't bother to read the applications).
I should expect to hear a decision by the end of this week (e.g., tomorrow). So much for being in bed tomorrow by noon BST!

All in all I was very dissatisifed with the process. The person I spoke to seemed like a brick wall: interested in asking questions but not interested in
listening to what I had to say.