Knowing that I was going to have to set stuff up again in 815 due to the project file changes, I blew away my install and unzipped 815 anew.
Setting up my project went fine...until I brought up the Project Properties pane and tried to add some source directories (I had none; the ones that I picked in the new project wizard weren't kept/were blown away/something), the OK button is grayed out as soon as I select a directory to add. (and so thus I have no way of picking a directory to add)
I have tried restarting IDEA a few times as well; no change.
I would file this as a bug in Tracker, but this seems really basic/necessary to do anything in IDEA, and it sounds like some people are using 815, and so clearly must not have hit the same problem. (basically, I'm trying to safeguard against me just being an idiot about something before I file a Tracker issue)