I recently configured FBA on a web application as a proof of concept.
I modified the 3 web.config files for sts/CA/webapp. I created the site collection, and I can log in and add fba users. Initially I could only login as the farm admin, but then I added authenticated users to the User Policy with full read, and then users could login.
However, after they login in, they get access denied when they try to access a list or library. They seem to be able to browse to other areas of _layouts. They also have full control to this site, so I'm not understanding why they can get to some areas but not others.