To answer your questions:
1. According to 6.2 docs, No... RADIUS only
2. It is bound in the direction of which the user was authenticated/authorized.
i.e. An inside user going outside that gets authenticated going outside, will have his ACL applied to the inside interface, essentially.
3. The per-user ACL overwrites the existing ACL's that are on the PIX for the duration of the users session
Hope that helps
-Bryan