I had the same issue. I follow the detailed instructions (as I have in the past for an upgrade), deleted the necessary files and kept the important ones, uploaded the working version this morning of 2.3 and I went to my admin page and I was told that my database was out of date, I need to upgrade.
I missed the message about it taking a while, so when I clicked upgrade now, it came to a white screen and I soon after refreshed. That was my mistake. Now I am getting database errors and duplicate entries;
WordPress database error: [Duplicate entry ‘1-category’ for key 2]
Starting to freak out a little bit, don’t know if it is still working in the background or if I need to do a fresh install or what…